I've had people request viability rankings for Gen 9 Pure Hackmons, and I don't think that's feasible currently because there haven't been enough high-level games to know what mons possess minor niches, and offenses/bulk to an extent are significantly less important determinants of viability than Speed/typing (meaning there are a lot less viable mons than in the more playable generations of PH). I tried making a ranking nonetheless, albeit with mons' placements being less concrete and individual ranks indicating a larger gap in viability than would be indicated on a viability ranking. I also added explanations for placement since some of them might not be super obvious at first glance.
General (Non-Wonder Guard)
S Rank
S1
Regieleki (Clearly the best at running Neutralizing Gas/Comatose + Sleep Talk + Revival Blessing/Shadow Tag item removal/No Guard sets. You can slap 3~4 Regieleki onto a team and it'll work reasonably well. Gets a good bit more usage than everything below it)
S2
Blissey (Imposter is absolutely insane thanks to granting Revival Blessing PP every time you come in. Innards Out is also meta defining)
Chansey (Blissey echo, both have their respective merits though. Blissey's a slightly better Imposter user since you aren't bluffing anything with Eviolite in a Neutralizing Gas metagame (you REALLY want Ability Shield), and Chansey's a better Innards Out user because at minimum Defense you have ~45% less physical bulk than Blissey does)
A Rank
A1
Arceus (Last Respects immune + is bulky and fast at the same time. Very good defensive utility)
Audino-Mega (Last Respects immunity + Fighting neutrality/only Poison & Steel weaknesses make for an insanely good typing)
Mewtwo-Mega-X (Beats everything with time and good positioning with Last Respects + coverage (+ Corrosive Gas/Sticky Web support) - without needing to boost beforehand. This alleviates 4MSS enough that MMX is significantly more effective than any other sweeper imo)
A2
Arceus-Grass (Spore immune Magic Bounce/Prankster/whatever else you might want that's not Wonder Guard)
Eternatus (Toxic Spikes absorber, Black Sludge + Trick user, great statball)
Slaking (Huge Power Extreme Speed OHKOes Regieleki, Last Respects immune, has Arceus-tier physical bulk which lets it run surprise defensive sets, can probably run Gen 7-esque Innards Out sets if it really wants to)
B Rank
Aerodactyl-Mega (No more Zacian-C to compete with, fast Shadow Tag sets are actually pretty sick. Rock/Flying typing comes in handy more often than you'd think, being Extreme Speed/Fire move-resistant/Spikes-immune)
Electrode-Hisui (Does Regieleki things while being Spore-immune)
Groudon-Primal (Can be a wonky Shadow Tag trapper/setup sweeper with Bitter Blade, though the latter is inconsistent and requires good plays in the matchups you realistically can win with it. Hadron Engine's neutralized by Neutralizing Gas now which sucks for it)
Mewtwo-Mega-Y (Pretty cool Shadow Tag trapper, doesn't do much else though. Some funky sets I haven't tried, like No Guard coverage, could also work)
Ting-Lu (Better bulk than Mega Audino but has a somewhat less practical typing, especially in the late game where Last Respects users can break through it)
Venusaur-Mega (Magic Bounce user that absorbs Toxic Spikes/can Trick Black Sludge etc. while being Spore immune)
C Rank
Arceus-Ground (see below post, also outspeeds Regieleki with Choice Scarf + blocks the occasional Double Shock from Regieleki)
Calyrex-Ice (Refrigerate FakeSpeed OHKOes Regieleki, beats Tera Ghost)
Diancie-Mega (Pixilate FakeSpeed almost always OHKOes Regieleki, beats Tera Ghost, also hits MMX for SE + Fairy coverage is great against certain Wonder Guards)
Deoxys-Attack (Faster, substantially frailer Mega Mewtwo Y. Lack of bulk can actually be a positive because you dissuade Imposter from coming in if you're a Shed Shell/Ghost-type Wonder Guard)
Giratina (Fat untrickable Ghost-type)
Gourgeist-Super (Fat-ish Ghost-type that's immune to Spore)
Gyrarados-Mega (Huge Power Jet Punch snipes Regieleki from half, Last Respects resist)
Kyurem-Black (See Calyrex-Ice)
Sceptile-Mega (Fast & Spore-immune, lets you run Choice Scarf Shadow Tag to some effect. With 3 Spikes layers you actually KO Regieleki with Headlong Rush)
Zoroark-Hisui (If you really wanna cope vs Last Respects you can probably run this as a Shadow Tag/Last Respects-immune Magic Bounce user. Knock Off Regieleki 2HKOes with item though)
Wonder Guard
S Rank
S1
Regieleki (Does fast Wonder Guard things better than anything else, convenient typing as well)
S2
Audino-Mega (Last Respects immunity + Fighting-type neutrality/relatively inconsequential weaknesses in Steel & Poison/good bulk)
A Rank
A1
Arceus (Good typing, Last Respects immune vs Neutralizing Gas users once Ability Shield (if ran) is gone)
Calyrex-Shadow (Good Shadow Tag-immune typing, really fast. Better as a fast support Wonder Guard than as a sweeper though. Ghost weakness does suck but Shadow Tag immunity is often worth it)
Kartana (Spore-immune + good Wonder Guard typing. Hits hard (especially with STAB Gigaton Hammer), has alright physical bulk)
Ludicolo (Spore-immune + good Wonder Guard typing for a Grass-type. Can customize Tera type unlike Ogerpon-W)
Slaking (Arceus clone, can slow pivot/Wish slightly more effectively)
A2
Arceus-Fairy (Good typing, competes with Mega Audino though)
Arceus-Water (Good typing + decently fast. Competes with Mega Swampert/Dondozo etc. though)
Escavalier (slower than Mega Scizor, the bulk difference doesn't matter much in practice when both are OHKOed by most Fire move users, and Mega Scizor itself competes with Kartana as a hard-hitting Fire-weak Wonder Guard)
Ferrothorn (Good typing + very slow pivot but competes with Kartana)
Muk-Alola (Good typing, weakness to Fissure/Ground coverage and weakness overlap with Regieleki does hurt though)
Sableye-Mega (Good typing but it lacks defensive utility against Neutralizing Gas users after Ability Shield is removed)
Swampert-Mega (Good typing, competes with Arceus-Water)
Zoroark-Hisui (Good typing though Dark weakness hurts)
B Rank
Dondozo (Better physical bulk than Arceus-Water goes a long way in a Last Respects-centric meta, even if Dondozo's slightly less effective overall imo)
Gyarados (Good typing, Spikes-immune, is Stealth Rock-weak + competes with Arceus-Water/Mega Swampert/Dondozo though)
Flutter Mane (Competes with Calyrex-S + is Ghost-weak, would be a lot higher otherwise)
Ogerpon-Wellspring (Locked into Tera Water so you can't Tera Ghost out of Shadow Tag and is therefore more dependent on Shed Shell than it would like)
C Rank
Arceus-Ghost (Ghost weakness sucks, use Zoroark-Hisui instead unless you wanna eat Dark moves more easily for whatever reason)
Blissey (The meta is VERY physically oriented)
Eternatus (Isn't actually weak to much besides OHKO and coverage. Absorbs Toxic Spikes and is a fast statball)
Farigiraf (Slower/bulkier Zoroark-H that's also weak to U-turn/random Bug coverage. Not fully outclassed by Meloetta because physical attacks are much more relevant than special ones and Farigiraf is slightly physically bulkier)
Gengar-Mega (Absorbs Toxic Spikes, worse Calyrex-S otherwise)
Groudon-Primal (Saw it once, Ground STAB vs Regieleki and statspread make it an ok enough Shell Smash sweeper/early game bulky Wonder Guard. Can't be worse than the other crap in here)
Meloetta (Slower/bulkier U-turn-weak Zoroark-H)
Ogerpon-Hearthflame (Not U-turn weak unlike Ludicolo/Ogerpon-W, and not Fighting-weak like Kartana/Ferrothorn. Being locked to Tera Fire kinda sucks)
Pidgeot-Mega (Non-Gigaton Hammer/Collision Course/Dark coverage-weak Last Respects immunity)
Pheromosa (Non-Ground weak fast Wonder Guard)
Scizor-Mega (Simultaneously less slow than Escavalier, not significantly bulkier than Ferrothorn while being affected by Spore, and weaker than Kartana)
Scovillain (Slower Ogerpon-H, customizable Tera type)
Venusaur-Mega (Good typing outside of No Guard, absorbs Toxic Spikes and is immune to Spore)
Lopunny-Mega
UR -> B
UR -> A-
UR -> A-
UR -> A-
UR -> B (wg vr)
