S
A+
A
A-
B+
B
B-
C
S rank reasoning:
Aegislash is probably the best pokemon in the tier right now, and it's easy to see why. It's stupid splashable and checks a lot of boxes while also being demonic to handle defensively. Hippowdon is the flagship balance/BO mon being a stupid good rocker, weather stopper, Zeraora counter, and soft checking so many things. Volcarona is IMO the most terrifying sweeper to face and the one pokemon that can turn the game around with a single turn. Fire/Psychic/Grass coverage is surprisingly tough to deal with, and you cannot discount its ability to run Bug Buzz or bulky Roost as well. Volcarona's presence is why I have Azumarill two ranks higher than Primarina. CB sets have literally 0 switch ins, and Aqua Jet is so so nice for Volcarona (among others).
Other things (not gonna talk about all mons): Terrakion is somehow even better and borderline broken despite the severe power creep. The lack of Slowbro and Palossand is noticeable, as Hippowdon/Aegi are no checks to this behemoth. Tapu Bulu brings insane support with Grassy Terrain and can be a fearsome breaker with CB. I would put it in S, but terrain can work against you, and it always is walled by a select set of mons depending on its coverage. Steela/Guss are the faces of balance, but Steela is hard stopped by Magnezone, and finds itself spamming Leech Seed more often than I'd like. Gengar is broken.
Stall is scary good right now, and while stuff like Terrak/Conk will always threaten it, I find it to be extremely versatile and can outlast most teams. That's why I have Chansey at A. Bisharp and Mamoswine are also two pre-DLC mons that got better. Cobalion is unseen, and most teams use Steela > Skarmory which makes Mamoswine a lot tougher to handle. Victini is also the best scarfer ever and I love it.
Alakazam has been underwhelming. It's cool under Psychic Terrain, but stacking it with Lele just opens up a bad Steela/Sciz/Tini weakness that's hard to cover. The Thundy twins also kinda suck. I think Thundy-I is better cause that speed tier is clutch. Being revenged by Terrak is simply unviable. Keldeo has been scary to deal with since Slowbro left and Vern vanished. Salamence is slower and hit hard by Specs Hydro, and CM 3 attacks (Air Slash) kinda snuffs teams relying on Grass-types to check it. Tentacruel is jesus and owns Celesteela.
Sun is alright and struggles mightily with opposing Victini and Rock-types. They often rely on like, Hat to check Terrak/Lycanroc which is a joke. Hydreigon/Latias make Venusaur a lot less scary too. Hippo also owns it. Rain outright sucks. Hail is neat cause Veil is Veil and Arctozolt can be really annoying. But without Hawlucha, Veil has gotten a lot easier to deal with.
Glowbro/Glowking are uncommon but annoying as hell to deal with. Same with Suicune/Toge. Staka is a shitty Steela but TR can fuck up an overzealous offense. Webs are annoying to deal with but often lose to lead Aegislash. Lastly, MMQ sucks now and that makes me sad.