In standard OU, Accupressure is held back by the fact that there's not many users, most of them are fragile-ish, and it requires extraordinary luck to start seeing much pay-off -even if you get an Evasion boost first thing (1/7 chance) there's no certainty the enemy will be impressed. Shuckle is the only user with enough durability to not be concerned by the possibility of something switching in that requires it switch out: if you're using Toxicroak and it gets an Evasion boost, is it worth staying in on Honchkrow on the chance it won't instagib you, while you're struggling to do real damage to it if you attack?
However, in this meta the first time you get lucky with an Evasion boost, you can instantly cart it off to any member of your team. Shuckle can sit there Acupressuring itself for multiple turns, or just keep switching in and Accupressuring opportunistically on some portion of the enemy team, and pass off not only every kind of stat boost there is but in particular those random evasion boosts will just stick around indefinitely until either a team member is KOed or something is done to remove the team's stat modifications. (Forced-switch move, Haze, Topsy-Turvy, etc)
Or put another way: in normal play, Accupressure is too random to be worth bothering with (Shuckle resents every Special Attack, Speed, and for some builds, Attack or Accuracy boost it gets, which is up to a 4/7 chance of being a wasted move!), but here since any boost you get can then be passed off to whoever will benefit on the team, it's not randomly worthless, it's just unpredictable what benefit you'll get. If Accupressure is reliably useful, people will use it. If it sees use, the Evasion boost will come up regularly. And since they can always pass it on, it can be shuffled onto really problematic Pokemon -or from one really problematic Pokemon to the next. Imagine swapping back and forth between Slowbro and Amoongus for Regenerator healing until the enemy misses, at which point you get in a free move, and go back to switching until they miss again. If the enemy doesn't have some way of resetting or ignoring your Evasion boost, this is just stupid and not really fightable with any kind of skill, and even a team that has such things may find that once its 2-3 guys that can put a stop to this crap are gone, the rest of the team is screwed.
Maybe it'll turn out to not be a problem, but this is really a completely different context from OU in terms of Accupressure's relevance, in the same way that Mud Slap, Sand Attack, etc are jokes in normal play and need to be banned here.