(All the stats and my rambling are so long they don't fit together in one post so I've split them up in the way that reads best, sorry)
Before talking about nominations for specific Pokemon, I want to talk about the two biggest shakeups to SM since the days when it was current gen: the rise of Zeraora and the retroactive adoption of Choice Band Genesect:
Zeravolution
Winners:
Losers:
Undoubtably the biggest change to post-current gen SM has been the steady rise of (Assault Vest) Zeraora, which we've continued to see the effects of over the past year. In fact I'd argue that almost every change in viability we're seeing is down to Zeraora, as you'll see in this post. Tapu Fini, who already had a strong argument for being the best Pokemon in the format, with Zeraora has cemented that position. Tapu Koko is now far less reliable a check even before Calm Mind boosts, with Zeraora safely able to limit its damage with Snarl, while Fake Out stops it or any other threatening attackers as Tapu Fini sets up. While Incineroar is obviously quite good with Tapu Fini, Zeraora is the superior Fake Out user and generally more proactive, all down to its Speed. Zeraora's Speed is actually insane in SM, as unlike in SS where there's Prankster Tailwind with dynamic turn order everywhere, it will just straight up be the fastest Pokemon on the field the vast majority of the time (I think Choice Scarf users are a bit underutilised now as an exception to this) and still outspeeds a number of Pokemon even in Tailwind, an important one being that Zeraora is still the faster Fake Out than Incineroar even if it has Tailwind.
The other already top-tier Pokemon benefitting from Zeraora is the everpresent Landorus-T, which now finds itself as the most used Pokemon in the tier. Landorus-T fills a similar sort of role as a utility-oriented bulky pivot most of the time, with the different types of utility the two bring synergising extremely nicely as a complete package together. Landorus-T has Intimidate for physical attacks while Zeraora has Snarl for special attacks, with Zeraora's more vulnerable physical side and Landorus-T's more vulnerable special side both being patched up by each other. Both also cover each other's weaknesses, Landorus-T being immune to Ground-type attacks aimed at Zeraora, while Assault Vest Zeraora comfortably tanks most of the primarily special Water- and Ice-type attacks aiming for Landorus-T. One exception to this is Mega Metagross's Ice Punch, but this is where a notably synergy between the two comes in: Zeraora can Volt Switch after Metagross Mega Evolves but before it attacks, letting it safely pivot out and bring in Landorus-T for Intimidate (even if it was originally in the other slot and just switched out), and even if the Metagross predicts this and uses Ice Punch on the Zeraora, Landorus-T typically EVs for this and so will survive and can activate its 50% berry to stay relatively healthy still. Another important thing to note about these two is their capacity as leads, due to the aforementioned reasons. With damage mitigation on both sides of the spectrum, and both able to pivot, they are great for adapting to almost any opposing leads, but also something specific that's important is Zeraora's ability to near guarantee with Fake Out that Landorus-T safely gets Stealth Rock up, facilitating the "doubles handshake" that often occurs in games. These two Pokemon work fantastically together (especially in combination with Tapu Fini and some of the other Pokemon I'm about to mention), but also notably they work far better together than either do with Incineroar instead. Zeraora and Incineroar together gets double Fake Out for setup, but stacks Ground-type weaknesses and often leaves you without a resist without Landorus-T; Incineroar and Landorus-T is okay and has been used a lot before, but the double Water-type weakness is quite weak to Rain, while the combination can be a bit passive at times due to both being on the slower side.
If you look at the selected usage for 2024 then you'll see Tapu Fini and Landorus-T had 50% more uses than any other Pokemon, these two have been elevated so far by Zeraora that there's a real argument to be had they should be alone in a tier above the rest. However, they're not the only Pokemon to benefit from Zeraora, Volcarona and Mega Salamence being another couple of major examples. This largely comes down to similar reasons as for Tapu Fini, they're both setup Pokemon that greatly appreciate Fake Out, and have far better synergy with Zeraora than Incineroar. The synergy between Volcarona and Incineroar is obviously bad: so bad that I'm not sure it's ever actually been brought to a serious tournament match. Mew also exists as a Fake Out option, and access to Transform shenanigans, but is just not as good of a Pokemon as Zeraora, while Zeraora having the faster Fake Out and Snarl to further facilitate setup is better for Volcarona being able to consistently set up. While Zeraora is not great at KOing Tapu Fini itself, what can often happen is it uses Snarl while Volcarona uses Quiver Dance to stop Tapu Fini from getting too strong from Calm Mind, keeping Muddy Water damage to a manageable amount, and then once Volcarona is sufficiently set up it can deal with everything else on the opposing team while Kartana can deal with the +0 SpA +6 SpD Tapu Fini for it. Incineroar is much more palatable with Mega Salamence, but Zeraora is also the better Fake Out partner there. A key difference again is the Tapu Fini matchup, Salamence appreciates some help due to its ability to tank hits and retallitate with Moonblast, with Incineroar able to force a Protect with Fake Out but otherwise giving it free reign. Again, Snarl can help in setup race situations, though in this case Volt Switch can also sometimes deal enough damage to put Tapu Fini in range of a killing blow from Salamence. A similar situation can happen with Landorus-T, as while it typically doesn't threaten Salamence the Intimidate is annoying for Dragon Dance, where HP Ice can put it range for Salamence (though two HP Ice can also do the job in this case). Even for non-Dragon Dance Mega Salamence sets Zeraora is still the better teammate though, due to the aforementioned matchups along with others such as being better into Tapu Koko or opposing Zeraora.
Tapu Koko's downfall should be news to no-one at this point, Zeraora is a far superior partner on Tapu Fini teams, while against them it makes Tapu Koko far less effective. There are still reasons to use Tapu Koko, such as its heavier firepower, or ability to remove Misty Terrain for teammates like Kommo-o, but it's obviously worse off now. What may come as a surprise, however, is the similar fall from grace of Incineroar. The heel used to be arguably
the face of SM DOU, even healing from Stealth Rock to some's dismay, but now it finds itself in a weird place. As I've went into more detail above, Zeraora + Landorus-T is generally a far better pairing than anything involving Incineroar, and with any of the number of great setup Pokemon in the tier Zeraora is the clear choice. A notable knock-on effect is the rise of Volcarona from Zeraora means people are increasingly using that as their Fire-type instead of Incineroar (Incineroar being a Fire-type only neutral to Bug Buzz also harms it on the front of being a check to Volcarona), further pushing it down. The other main shift we've seen due to the rise of Zeraora is Kingdra (though importantly, not Rain as a whole IMO) dropping off. Previously, many goodstuffs teams would consist of Tapu Fini and then 5 Pokemon obliterated by Muddy Water (Kartana resists, but that just means it takes as much as anything would neutrally), making Kingdra a complete menace to go up against, and often meant the game was lost if its teammates like Tapu Koko could sufficiently deal with Tapu Fini for it. However, Zeraora is a completely different story compared to the teammates like Tapu Koko and Incineroar it takes the place of. While not a natural Water-type resist, Assault Vest and EV investment provides Zeraora enough bulk to sufficiently tank a hit (or two, especially with a Snarl inbetween) when needed, which can often be enough to change the game. A -1 Kingdra is much easier to deal with as it relies heavily on picking up KOs, while Zeraora's ability to give Kartana enough breathing room to safely set up a Tailwind can often be enough to win the game. Many Rain teams, especially the Kingdra ones, struggle heavily against Calm Mind Tapu Fini, with Zeraora able to help it snowball (e.g. by using Fake Out, taking a big hit, switching out, and bringing it back in to Fake Out again, as opposed to Incineroar which will Fake Out once and immediately die to the first hit) and win that way as well.
Genesects & Violets
(That is a pun based on Blood on the Clocktower that nobody other than me will get)
Despite not having anywhere in the same stratosphere the amount of influence as Zeraora, (Choice Band) Genesect is another Pokemon that has popped up retroactively as in the other gens because of its success in SS. I don't know if there's any other Pokemon that has changed too heavily directly as a result of Genesect, but it's a strong Pokemon worth considering. It does the same thing it does in other gens, Choice Band U-Turn is strong, and benefits from the most common Fire-type, Incineroar, not resisting it, though a nifty thing about Genesect in SM in particular is that Extreme Speed is useful for picking off the other most common Fire-type, Volcarona. Genesect takes at most around half from the five most common Pokemon in Landorus-T, Tapu Fini, Kartana, Mega Metagross, and Zeraora, so is often great at trading positively due to Choice Band and Download in a meta without many immediate hard hitters. Unlike most other pivots in the metagame, which when clicking U-Turn or Volt Switch are focused mainly on maintaining momentum rather than dealing damage, Genesect's rare ability to actually threaten as a pivot helps guarantee progress, while still pairing nicely with the aforementioned bulkier, more passive pivots to help bring it back out again to continue the cycle. With Extreme Speed offering unique pressure to snipe weakened Zeraora before it can be annoying, and options for its 4th moveslot like Blaze Kick to hit Mega Metagross harder or Gunk Shot to nuke Tapu Fini, Genesect has an extremely well-rounded kit that offers something different than practically any other Pokemon in the meta.
Now onto some formal nominations/votes and my (shorter) thoughts on them:

Incineroar
Tier 1 -> Tier 2
As I've already went in depth on Incineroar has had a large part of its niche as a Fake Out pivot taken by Zeraora, while Volcarona has risen to become serious competition for the Fire-type slot (in the selected usage, the two are even right next to each other in usage). Incineroar is no longer a Pokemon you can slap on almost any team and it be the right choice (as it should be for Tier 1), you need to give actual thought to whether something like Zeraora and/or Volcarona is better because they often will be.

Zeraora
Tier 2 -> Tier 1
Again a Pokemon I've already discussed at length, in my previous post I was floating the idea of Zeraora being Tier 1 and I think 2024 has done enough to sell me on it. Usage puts it just on the border between the two, but I think Zeraora is absolutely strong enough to be in Tier 1. It is the best Fake Out pivot, but it also offers so much more, as its Speed is near unmatched and with BoltBeam coverage between Volt Switch and HP Ice, Zeraora is practically never in a bad spot. At worst it might be clicking Snarl, but with how great that is for so many teammates that's hardly a drawback. Zeraora + Landorus-T is insane, Zeraora + Tapu Fini is insane, Zeraora is also amazing with other setup like Volcarona and Mega Salamence as well. I genuinely think you cannot go wrong with Zeraora, before I thought that its gig as a Tapu Fini sidekick meant it should be Tier 2, but it's actually just that the two are so bonkers together you don't see much Zeraora without it, and it can absolutely do the same great things with other Pokemon like the ones mentioned earlier if you really want to go without Tapu Fini.

Kartana
Tier 2 -> Tier 1
I said in my last post that this was years overdue, well add another year to the list. Kartana was the 3rd most used Pokemon in the selected usage, as I've said before it is just the best Tailwind Setter and best (Calm Mind) Tapu Fini check, while being a great Pokemon with or without Z-Move. Kartana didn't need Zeraora to be all that, but it definitely doesn't complain about Zeraora taking out Tapu Koko as competition to be the best Tapu Fini killer. The two Pokemon it really struggles against have been recent rises in Volcarona and Mega Salamence, but ironically Kartana is actually one of their best partners due to its aforementioned ability to deal with Tapu Fini. Kartana isn't even really
bad into any of the most used Pokemon, Incineroar is weak to Sacred Sword and Mega Metagross doesn't do much to you either. Did I remember to mention Kartana is the best check to Tapu Fini? Seriously, Zeraora doesn't actually kill it, and Tapu Koko struggles to kill it when there's a Zeraora beside it, nothing is on the same level as Kartana when it comes to checking Tapu Fini, the literal best Pokemon in the tier.

Diancie
Tier 2 -> Tier 3
Not much to say here, Diancie really should have dropped last time, if anything the question is should it drop to Tier 4, but I think Tier 3 is fine for now. The rise of Volcarona and Mega Salamence does feed Diancie enough ammunition that I wouldn't drop it that far just yet, even though I don't think it's that great.

Volcarona
Tier 3 -> Tier 2
Another Pokemon I discussed earlier, in the selected usage this Volcarona almost had as much usage as Incineroar, how crazy is that. It's actually not that crazy when you watch games with it, this thing is an absolute threat that runs away with games on the regular. The one real thing going against Volcarona is the 4x weakness to Stealth Rock, but when Landorus-T and Tapu Fini (I think support sets with Heal Pulse are really good with Volcarona) are both on your team already and can fit it that's a small ask. It's the same with Zeraora for Fake Out, you really don't need to go out of your way to support Volcarona, the best Pokemon already do that. While not quite as insane as Calm Mind Tapu Fini, Volcarona trades bulk for speed and power, offering a slightly different kind of setup but still incredibly potent, and puts on enormous pressure due to how big a threat it is after even just a single Quiver Dance.

Mega Salamence
Tier 3 -> Tier 2
Mega Salamence is a pretty clear 2nd best Mega now in my eyes, not as splashable as Mega Metagross but definitely a cut above everything else. The biggest reason for this is what also makes Mega Metagross the best: the ability to put it on many teams without much support. Like Mega Metagross, Mega Salamence has great all around stats, beginning with an excellent Speed tier usually only beaten by Zeraora/Tapu Koko, to respectable defensive stats (bolstered by Intimidate pre-Mega), and a high Attack stat boosted by an offensive ability. While Salamence's typing can be a hindrance into Pokemon like Tapu Fini, Mega Metagross itself, and Zeraora, on the other hand it is great into other common Pokemon like Landorus-T, Kartana, Incineroar, and Volcarona (notably being one of a select few to resist both its STABs. With Dragon Dance being another strong setup Pokemon requiring only the likes of Zeraora that you'd want anyways, or mixed sets offering immediate damage and coveted access to Tailwind (while beating the most common setter in Kartana), it's easy for teams to find a place for Mega Salamence without dedicating too much towards it.

Kyurem-Black
Tier 2 -> Tier 3
Kyurem-B has had it rough for a while, Stealth Rock everywhere massively limits the effectiveness of Assault Vest sets (while unlike a Volcarona or Mega Charizard-Y they aren't quite worth dedicating Defog for), while offensive sets struggle due to its weaknesses to common Pokemon like Mega Metagross and Kartana. Incineroar is quite annoying for any set, Intimidating and eating any hits from physical sets while Knock Off neuters Assault Vest sets. The rise of Genesect is also not the best, but I think Kyurem-B was already on the way down anyways, especially as the Tapu Koko teams it worked best on have fallen away with the rise of Zeraora. Kyurem-B still has massive stats, while BoltBeam coverage is still great and there's strong nuke potential with Z-Moves, but similar to what happened to it in SS I think Kyurem-B is definitely on the way down.

Genesect
Tier 3 -> Tier 2
Genesect is another Pokemon I've rambled about earlier, and while it hasn't made quite the same waves as Zeraora I think it's still a surprisingly solid Pokemon. Like I said before, Genesect is a rare hard hitter in a tier with a lot of Pokemon that are either more passive or require setting up first. Mega Metagross and Kartana existing, with even Celesteela too to a lesser extent, there is a surprising amount of competition as a Steel-type (yes Kartana is not a "true" Steel-type but stacking two 4x Fire-type weaknesses is not it), but I think Genesect still does enough to be if not Tier 2, then at least on the high end of Tier 3, and the usage backs that up.

Celesteela
Tier 4 -> Tier 3
Celesteela is a really interesting Pokemon though, most of it's success has still come from the basic Leech Seed set, which has indirectly gotten better due to meta shifts. Zeraora has taken Tapu Koko out the way for Celesteela, one of its biggest threats, while instead Volt Switch isn't that threatening and also switches it out to something else so it can't be used repeatedly. Looking at the other top Pokemon, Landorus-T, Tapu Fini, Mega Metagross (without a relatively rare Thunderpunch), and Kartana all don't really threaten it either. Incineroar is very much a problem, and while Volcarona or Zygarde can be a problem, Wide Guard leads to stalemates that can sometimes be beneficial with Leech Seed or the right partner. With two out of the three of those weak to Stealth Rock (and Leech Seed promoting a lot of switching to rack it up), Celesteela is actually pretty effective as a defensive win condition in the current meta.

Aegislash
Tier 3 -> Tier 4
There are at least 3.5 better Steel-types than Aegislash in Mega Metagross, Kartana, Genesect, and Celesteela. Celesteela does the whole defensive Steel-type thing a lot better, and aside from that I don't see too much that Aegislash does. Stance Change is too much work to play around for the reward, and while you do stonewall Kartana and kind of beat Mega Metagross (but Stomping Tantrum and Stance Change make that not so simple), that's not enough to make up for how bad its matchups are. Landorus-T beats you, Zeraora beats you, Tapu Fini uses Calm Mind unless you can get a Toxic off, Incineroar should beat you, etc. etc. Anything Aegislash does, Celesteela probably does better, like it's still good into Kartana and Mega Metagross, and can Leech Seed the other stuff without needing to worry about terrain for Toxic, and also has Wide Guard for any shenanigans for that. Also, while Mega Venusaur teams often opted for Aegislash in the past, Genesect is the typical choice nowadays as a much more proactive Pokemon. 37th in usage from the selected dataset, Aegislash is definitely too niche for Tier 3.

Amoonguss
Tier 3 -> Tier 4
I feel like in every tier people overrate Amoonguss relative to how good it actually is, given how many times I've had to argue for it to drop. Yes, Spore is a strong move, but it's not enough alone to make Amoonguss strong, especially in the tier where grounded Pokemon are immune to Sleep the majority of the time. Okay well what about redirection? Well it can be nice for setup but look at the most common setup teams and you won't find Amoonguss because that still isn't enough. In the case of Tapu Fini you can't redirect away Kartana which is one of the main things you'd want to redirect, and in the case of something else like Volcarona or Mega Salamence, you're generally much rather going to want Kartana yourself to deal with Tapu Fini (something Amoonguss is much worse at than it should be). Amoonguss has always had the same problem in SM: you're effectively forced to use Tapu Lele to be able to reliably Spore, and Tapu Lele is not
that great a Pokemon in the first place, which is not a worthwhile trade. The Mega Gardevoir Rain team, which successfully ran terrainless Amoonguss, has even fell away, leaving basically that one Tapu Lele/Amoonguss/Zapdos/Volcanion team that Amoonguss gets used on.

Ludicolo
Tier 5 -> Tier 3
Compared to other people I have a differing view on Rain currently, while it's true I was critical earlier of Kingdra not being able to run through goodstuffs teams as easily, I don't think that necesssarily means Rain as a whole is bad at the moment. I do think if you stick to an older team relying on Kingdra that struggles into Zeraora you'll have a tougher time now, but I've liked the Ludicolo/Mega Swampert style of teams such as from
variationonatheme's post, which when I ran into during SM Swiss caused me problems and impressed me. Mega Swampert is great into Zeraora, while Ludicolo is a Swift Swim user positive into Tapu Fini, and while individually both play different from Kingdra, facing two Swift Swim Pokemon together at once is a entirely different ball game. I think as a playerbase we've stagnated a bit when it comes to Rain teams, particularly with regards to seeing Choice Specs Kingdra spamming Muddy Water as
the optimal way to go, and while I know this newer style of teams still has room to be fully optimised, I still believe a drop for Rain is premature. Even though Kingdra has gotten worse I'm still hesitant about dropping it because Rain as an archetype is just that powerful, and needs to be respected in a way that most Tier 3 Pokemon don't, let alone Tier 4 which is Pokemon you don't really need to actively consider much at all.

Politoed
Tier 3 -> Tier 4
On Politoed vs Pelipper, I think Pelipper is the clear choice, and if you look at both sets of usage for 2024 then Pelipper has over double the usage of Politoed. Pelipper is obviously better with Mega Swampert for Earthquake, but even aside from that the ability to set/match Tailwind, and beat Kartana 1v1 instead of losing like Politoed, is generally more important for Rain than access to Helping Hand or being able to tank a Volt Switch From Zeraora. With such a gulf in usage I think Pelipper deserves to be ranked a tier higher than Politoed.

Mega Gardevoir
Tier 3 -> Tier 4
Mega Gardevoir is nice specifically on the Araquanid SemiRoom type team, but outside of that I don't think it's that great. Mega Gardevoir lacks the bulk even with investment to reliably set Trick Room against the many physical attackers in the tier without taking a hefty amount of damage, which is not a great use of your Mega, and while Pixelate Hyper Voice is nice it doesn't quite make up for that weakness. Outside of Trick Room, Mega Gardevoir is still too slow that it runs into the same problems due to its physical frailty, and while Tailwind and Sticky Web can unlock more of its potential, it's a lot of commitment which relegates Mega Gardevoir to basically that one aforementioned team style where you can justify it. I would compare Mega Gardevoir to Mega Charizard-Y or Mega Salamence, which have better physical bulk and better resistances, while Tailwind rather than Trick Room is more useful for most teammates, so are generally stronger at fulfilling the niche of a spread attacker Mega (with speed control) while requiring less support, solidifying the fact that Gardevoir needs to be used with specific teammates like Araquanid to be worth it.

Mega Scizor
Tier 3 -> Tier 5
I voted Mega Scizor down to Tier 4 last time, since last time I think it's gotten even worse. Mega Scizor always had to compete with Mega Metagross being better, but its ability to snipe Tapu Koko with Bullet Punch and not be terrible into Incineroar despite the 4x Fire-type weakness made it a solid enough option on specifically the Tapu Koko/Gothitelle/Kommo-o builds it worked on, but those are tailing off and Choice Band Genesect exists as a Steel-type with a strong priority move. Extreme Speed is better into Zeraora and Volcarona which have risen up, but Genesect is also just generally better I'd say, its Speed is far better and Choice Band even without Download hurts, while U-Turn keeps momentum whereas Mega Scizor is liable to getting Intimidated and being too passive. Oh there's also the whole getting another Mega with Genesect thing, but even that opportunity cost aside Mega Scizor is basically just a worse Genesect. Mega Scizor had one (1) use in the selected usage, I can easily see voting this Unranked in the future.

Mega Manectric
Tier 4 -> Tier 5
I nominated this down in my last post, Mega Manectric is so outclassed by Zeraora I think even forgetting about the Mega slot Zeraora is probably still just better. Only one (1) use in the selected usage says it all, I'm actually in half a mind to just vote Unranked right now on this because I just don't see the reason it would be worth using. The SemiRoom teams Mega Manectric has been used on before have been rare for a while already and I don't see any reason for them to be getting any better.

Mega Latias
Tier 4 -> Tier 5
Mega Latias used to be a personal favourite of mine but it has just gotten worse and worse. Zeraora Snarl stops it from ever getting off the ground, Genesect completely owns it, and now Volcarona owns it as well. With a non-zero amount of Toxic existing that immediately shuts it down as well (though you don't even need that these days due to the aforementioned Pokemon), it's not difficult to prevent Mega Latias from setting up successfully. Unlike Tapu Fini or Volcarona, Mega Latias also really requires multiple boosts to do anything at all, and uses a Mega slot for the troubles, so just all around a pretty terrible deal in a similar vein to Mega Manectric, but not quite as extreme. Only 3 uses in the selected usage, of which 2 were probably me and I'm voting it down.