Played a fair bit of the meta.
Zygarde, Greninja, Mega-Metagross are all mons without reasonable counterplay.
Greninja has 3 separate sets, all of which have varying counterplay, and a wrong guess will lose you the game very quickly. Regular Greninja already speed-creeps most of the meta, beating the glut of megas at 120 base speed, bond can and will end the game in an instant, and while the sets do all reveal themselves relatively quickly, guessing bond and losing most of your Clef's HP to a Gunk Shot can and will happen. Mega Greninja is potentially the most overwhelming of the three major sets, as Flip Turn AoA removes a ton of would-be counterplay to the standard set, and still finds room on its set to snipe whatever checks you'd have.
Zygarde itself is almost brainless, as you just need to read Slowbro once with Toxic to effectively put it on a timer with Tarrows for the rest of the game. The second you do its forced to either bleed valuable momentum by clicking Slack to offset the chip, or just port immediately after coming in every time to minimize HP loss. There are other checks, notably the rising Gourgeist-Super, but all your counterplay barring Mega-Meganium is vulnerable to the same cycles that are extremely easy for BO teams to set up using Zygarde+Slowbro.
Mega-Metagross just has too many moves. Hslam/Tpunch/Ice Punch hits every single viable mon in the meta barring Aegi for either a 2HKO, or comes extremely close, and the last slot can literally be anything. I've been going Pursuit to effectively remove Slowking-Galar from the meta, but you can run PuP, Rock Polish (+ Adamant), Bullet Punch, Psychic Fangs for Mega-Chesnaught, Knock Off for Aegi, or basically anything you want. Even Grass-Knot is viable to snipe Slowbro extra hard.
A recent team I was using; got to 1495 before I lost a game due to misreading a Gren set.
https://pokepast.es/f42c3b495ead7d4b
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In terms of fun sets I've been using. CB Gourgeist is an extremely effective lure, letting you remove Clef from the game 30% of the time, and is a good mon in its own right. Being effectively the only viable Tarrows resist that doesn't require a mega slot and doesn't bleed momentum is really cool. Poltergeist is also an extremely clickable move, and Power Whip is weirdly good as a lot of folks are skipping out almost entirely on grass resists. Trick is also a free click once folks realize the set, as they'll immediately hard Skarm, which then unironically loses to you cause Sneak + SR will outlast Roost.
Mixnite is very good. Draco + Iron Tail + Fire Blast is simply not a combination teams can deal with, and while you need LO to actually secure KOs, you still contribute a lot to a team given a workable speed tier and Espeed in case you need to remove a low-HP gren. That said it requires a bit too good of hazard control to be great on any team not running MDia.
Speaking of Mdiancie, its excellent. Acting like a slightly weaker version of MMeta, you simply have the coverage and power to KO basically everything in the format. Slowking-Glar is the closest to a proper check, but like even then if you read it enough times with either Diamond Storm or Earth Power its really not a reliable answer. That said, you're also weak to literally every mon faster than you, and you don't really block hazards
that reliably.
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In terms of ability changes, pls give Dragonite an accuracy steroid of some kind, be it moving Drizzle from Drampa to it (and giving Drampa something like Fur Coat or stamina), No Guard, or just something on that end.
