I'll give my thoughts on some noms I disagree with so far as well as make a few of my own.
Bellibolt Keep B+: A few people are supporting of this thing rising to A- and I get it, but I think it has a few really bad flaws that make it very awkward to use, those being passivity and a weakness to chip, especially from hazards. First off, passivity. Bellibolt isn't bad at pressuring mons and getting momentum with Volt Switch and Toxic, but the big issue comes against setup sweeper. Its damage output is very underwhelming as it relies on Volt Switch (a move that prevents it from staying in) and Muddy Water (a move it lacks STAB on) to deal damage. Both of those struggle to 1HKO even targets that are weak to it. If you're trying to counter a NP Torn, it can legitimately just stay in, hit you for 50%, come back later and finish you off. Toxic is also just really not sufficient to hold setup wallbreakers back. If you're staring down an Iron Hands, it can still just SD and trade one for two or three because Toxic is just not fast enough to take it out before it gets out of hands. Bellibolt teams are playing slow enough that 1v1s against breakers like Hands or Hydrei are pretty much inevitable if your opponent looks for them and risk breaking your defensive core easily. These issues get much, much worse if you have to face Steel or Poison type setup mons like Scizor, Okidogi or Tera'd Sinistcha. As for its weakness to chip, the big issue that stands out here is that Bellibolt is neutral to so much that you can't really take hits from 50% since you won't resist them. Whatever wallbreaker you're trying to deal with, dropping below 80% with Rocks up is probably leaving you in a pretty scary position against stuff like Weavile, Quaquaval and even Gapdos. In theory, Bellibolt can punish U-Turn, but in practice, I feel like that leaves you very open to wallbreakers getting through it if it takes them with hazards up. AV Torn doesn't mind getting Static'd that much and the opponent can decide to play the long game, just getting Bellibolt into range of their wallbreakers. I guess what I'm trying to say is that Bellibolt leaves itself very open to trades and I find it doesn't make for very sturdy cores as a result if your opponent is willing to make some sacrifices for the sake of progress. I consider cores using Rotom-Wash can actually adapt to its lack of longevity better and actually use its ability to spread more instantly threatening status and deal better damage overall more efficiently. I'd rather see Washtom drop to B+ than see Bellibolt rise though if I'm being honest.
Ogerpon Keep B+: Only one nom to drop, but I've seen a few people hate on this comparing it to Meowscarada notably and I just gotta clear its name and explain. First of all, you have to be ready to invest your tera into it most games and that's a big investment. However, if you do, you end up with a wallbreaker with a crazy speed tier of 525 without any restriction and a damage output comparable to Rillaboom's. Ogerpon can get through regular Grass resists like Torn-T easily and access to Zen Headbutt makes Poison-types much less reliable answers to it. Swords Dance can end games extremely efficiently once its counters are gone because of just how fast and strong it is. I don't think comparing it to Meowscarada is very fair though and you probably shouldn't use Ogerpon primarily for its utility pivot value rather than its raw speed and damage output. Not that its utility can't be good, Encore especially can generate an insane amount of advantage. Ogerpon also has weirdly good bulk for its power which allows you to stay out of range of Weavile Ice Shard and Scizor Bullet Punch to an extent or to survive SE hits from AV Torn or Amoonguss if you want to trade. Anyway, its Tera reliance and somewhat lacking consistency probably keeps it out of A tiers, but I think it fits B+ and dropping it further wouldn't do it justice.
Alright now unto the noms
Weavile A+ --> S-: Not quite on the same level as Treads or Torn due to those being glues, but Weavile is simply a monster. Not only is it the fastest mon in the meta unboosted, already impressive for a wallbreaker, but its typing lets it act as excellent speed control, hitting both Torn-T and Meowscarada super-effectively and packing Ice Shard to hit common Scarfers like Hydreigon or Gapdos. This alone is already pretty crazy, but it's also one of the scariest wallbreakers on top of that. +2 Tera Dark Knock Off is ridiculous, one shotting relatively bulky neutral targets like Iron Treads and Rotom-Wash and even forcing mons like Quaquaval to be careful with their health. Seriously, Weavile can drop most offensive mons easily at +2 and it does that while being a speed-control option. It's very good at wearing down its Fighting type checks thanks to Knock Off's item removal and its superior longevity thanks to Boots. In general, these traits just make Weavile an incredible mid-game attacker and late-game wallbreaker/sweeper. This difficulty keeping it in check in the long run can often force certain Ice or Dark weak mons to Tera to get rid of the threat early, for example with Steel Tornadus or Hydreigon. This forced Tera can be very nice for Weavile's teammates and can even put you in extremely advantageous positions if you can call it out (You can probably afford to try to bait it out and switch since Weavile teams tend to play a bit on the slower side). This mon has shown itself to be a top tier offensive threat for multiple reasons in tournament play so far and the amount it adds to the teams it's on makes me think a rise is justified.
Quaquaval A- --> A: Quaval's current ranking does not accurately reflect how threatening of a wincon it is currently. It snowballs incredibly hard between Swords Dance, Moxie, Aqua Step and its wide movepool; you cannot afford to give it any breathing room or the game will likely end on the spot. Water/Fighting has a few decent defensive switch-ins in the current meta, but with great Flying and Dark coverage, most of these seem like fake answers, potentially requiring Tera or a resist berry. The only issue of note for me is that its setup opportunities are somewhat limited. Regardless, Quaquaval should be considered one of the main threats to keep in mind when building a team and A rank is more fitting of that. If that's not enough for you, then I'd also like to mention its great defensive utility. While it doesn't deal with much, Weavile and Arcanine-H can be some of the most difficult pokemon to switch into in the metagame and Quaval can provide you with a reliable switch-in to both which can be incredibly valuable.
Thundurus-Incarnate C+ --> B-/B: Nasty Plot sets are very good at breaking down standard balance cores that lack Speed besides Tornadus-T and Iron Treads. Its main niche over its Therian forme is that Thundy-I can outspeed Iron Treads. Its damage output is a bit lower, but it's good enough for what it wants to do, landing 1HKOs with Thunderbolt on common offensive Water-types unboosted, most slower offensive mons such as Scizor or Arcanine-Hisui at +2 and one-shotting Iron Treads and Amoonguss at +2 with Grass Knot and Psychic respectively. Basically, Thundurus-I is quite good at breaking down certain balance cores and can perform better than other pokemon C+ in my opinion.
Also got some drop noms
Meowscarada A+ --> A: Alright this one might not be well received, but I still want this to be acknowledged. Meowscarada feels like it's lacking something on every set and it feels too easily walled to be A+ rank. Boots and Scarf offer very nice flexibility overall, but have a very hard time actually forcing switches to set Spikes or Pivot properly. Torn-T and Iron Treads are the most common pokemon in the metagame and they can take Meowscarada's hits while also generating a lot of advantage if it Spikes or U-Turns as they stay in. There are also a lot of neutral targets that require chip before dropping into its range, a lot of Fighting-types that force you out and even something like Sinistcha can just stay in despite being weak to Knock Off. When you do properly force something out, the progress you make tends to be limited due to having to deal with really good switchins like Amoonguss, Okidogi, Iron Hands or Gweezing who can take your hits with ease. Sure you can get up Spikes, but I don't feel it comes in nearly often enough to be able to apply reliable pressure with those. Band is the opposite, it does a ton of damage, but when you run into some of the counters listed above, it feels really rough trying to properly wallbreak with it. At the end of the day, it's still Meowscarada, great speed control, good spiker, forces answers to it on teams, but I haven't felt it gets the value an A+ tier mon should get.
Scizor A --> A-: This feels really out of place, A- feels a bit high for me even. The main thing that has stood out about Scizor this whole gen is its relation to its health: any hits it takes will stick and it needs to manage it properly in order to setup an endgame sweep. With such a fragile win condition, you'd expect very high rewards and good consistency, but that's not really the case. Scizor has to rely on Bullet Punch more than ever with the overall speed tiers being higher, but it also has to use BP in a meta where Electric types like Washtom, Sandy Shocks, Thundurus and even tera'd mons like Torn-T are very common. You also have to deal with bulky targets like Iron Hands and Skeledirge that will often take multiple hits to take out. On top of that, a majority of teams carry Iron Treads which outspeeds, takes Bullet Punch rather well and can even hit common Scizor Teras like Fire and Steel super-effectively. This mon just has to get through so much to get results and I feel like that makes it rather inconsistent.