I'm gonna go through each of these mons, or at least most of them, and say what I've seen in recent meta developments.
S Rank
Clefable: Best mon in the meta. Teleport (especially with Wish) is busted. They're almost always spedef, haven't seen LO in a long time. LO needs to run CM to beat other clefs if they're fat. It's unbelievably splashable, but also a pain in the ass to play against. I love it and I despise it. Knock Off and Thunder Wave are also really nice atm.
Corviknight: The premiere Excadrill answer. Mostly been seeing bulky defog with Body Press to beat Bish and Drill. Bulk Up is still fairly solid but it's prone to being statused. Hasn't changed much.
A Rank:
A+ Rank
Aegislash: A bitch to play around. Nothing like going into a defensive Pex on a presumed CB only to get smashed by Specs Shadow Ball. Specs and Band are amazing, but SD isn't that great these days. SubToxic isn't that good but it's definitely annoying.
Dragapult: Wisp Hex Draco U-Turn is the best set rn. It hates the rise of spedef Clef and Zeraora is annoying but it's still solid. Specs is underwhelming, DD sets are a cool meme I guess. Scarf Dragapult is bad.
Excadrill: Busted on paper. Busted in practice if any of Corv / Mandi / Hippo are removed, but fairly useless if they're healthy. Band is cool on gravity teams, especially since it 2HKOs max physdef Hippo after like any chip at all. Lead sets exist I guess.
Hydreigon: NP is still decent honestly, just needs chip to secure the OHKO on spedef Clef with +2 LO Flash Cannon. Or just run modest and nuke it. Sub NP is too weak and scarf is bad. Still an absolute menace to every team, especially fat ones. Might work well in conjunction with Kyurem?
Kommo-o: dont care to write anything
Rotom-Heat: Annoying bastard. Pairs really well with Wish support from Clef. Just avoid Knock Off.
Toxapex: Fat piece of shit. Toxic Spikes are broken. Knock Off is a busted move.
Zeraora: Bulk Up seems like the best set rn, but mixed 4 attacks is also very good. The latter gets worn down pretty fast, unless of course it's paired with Wish Clef. Seeing a pattern here?
A Rank
Conkeldurr: Unwallable. A get out of jail free card against Terrak, Drill, Kyurem, etc. Nearly unstoppable with Wish support.
Ferrothorn: Very annoying, but can be kept down with Knock Off and Scald burns.
Kyurem: Specs is wild. Knock Off support makes it unwallable. A little hazard removal lets it come in for free and tear your opponent a new one, over and over. Sub Tect DD is a weird meme.
Mandibuzz: dont care to write anything
Seismitoad: This exists to beat Dracovish and get rocks up, and that's about it. Hasn't changed at all.
Terrakion: Can safely exist without Shed Shell after Arena Trap's ban. SD is best imo, Band is scary but too prediction-reliant. Scarf is meh.
A- Rank
Cloyster: Total bullshit. Autowins against a lot of teams and can skill through the rest with King's Rock. Love/hate relationship with this fucker.
Dracovish: Incredibly unhealthy effect on the tier. Will 6-0 any team lacking any one of Pex/Ferro/Toad and can still get past them through rain or repeated chip. Most brainless Unga Bunga mon in this tier, and that's saying something. Can't be trapped by Dug anymore, but Dug can't trap Pex anymore. Basically a draw. Same as always, otherwise.
Gengar: If you want a fast ghost breaker, ignore Dragapult and use this. NP is scary as hell. Slept on pretty hard.
Jirachi: Scarf is ok, but SubCM is really cool. Lots of teams have no good answer to it. Spedef with Wish is probably good since it dunks on Clef but I haven't seen it used recently. Also kind of a draw with Arena Trap's ban.
Sylveon: Who?
Togekiss: Sub NP is great. Mon has serious electric-type allergies but rips fat builds a new one. Scarf is meh. Appreciates TWave support.
In general, the best strat rn seems to be spamming status and Knock Off mindlessly so breakers can run through teams easily. Bulky Offense seems better than balance but both are solid. HO is mostly using webs and sometimes screens, and stall is very rare. Tier will probably improve as long as Melmetal doesn't come back.