Dondozo and Skeledirge will 6-0 you if you leave Dragonite in on them... hardly passive lol
well gee if these two specific pokemon check something busted then what's the problem!? You know avalugg did pretty good vs zygarde 50% why did we need to ban zygarde let's just all use avalugg! Except for the fact that even with no attack investment earthquake 3hkos skeledirge... awkward! Especially with reduces slack off pp, this gets dicey fast.
0+ Atk Dragonite Earthquake vs. 0 HP / 252+ Def Skeledirge: 146-174 (41.8 - 49.8%) -- guaranteed 3HKO
Yes, tera fairy will stop this onslaught, but using tera to check tera feels to me along the lines of "broken checks broken", which nobody wants a meta game to devolve into. Just because SOME pokemon can check something doesn't make it balanced. The difference between the avalugg comparison is that skeledirge and dondozo are actually good on their own but you get my point.
With tera, it's like the entire game is a 50/50 because they may just tera into something you didn't expect.
Let's say you're facing down gholdengo with a mon with earthquake. In a non tera meta, the question is "do I hit earthquake or do I try and read the ground resist/immunity coming in and try to smack that hard instead?" Usually you'd just hit eq in case the opponent tries to be cute and stay in predicting your predict. In any case, you've positioned yourself to be in a good spot here. Tera throws a lot of wrenches into the mix. What if it's tera flying and you just lose. Or maybe you try to thunderbolt dondozo but it uses tera grass or tera steel or whatever the hell and now you can't kill it anymore. It's not something you can really prepare for, and it's not something that you can read like a switch in. You're not gonna tell me that I should start throwing resisted hits at a pokemon because I think it
might tera into something. You're not gonna go "erm... why didn't you just use close combat on dragonite you knew it was gonna tera normal lol!!!"
Often times the way you beat tera is to just use your own tera in retaliation. Unless I'm insane. It's not even a true 50/50 it's like a 20/80. Tera's swing factor is way stronger than z moves, because at least you could usually infer what mon had a z-move (knock off was a dead givaway, and heatran was probably not holding a choice item, etc). While z-moves certainly had a swing factor (bloom doom on fire types comes to mind), you didn't just get to continue to beat bulky waters like tera grass lets you.
Also the comparison to low accuracy moves doesn't work. Since every pokemon on a team can use tera, you never know for sure when you're gambling. Sure, you might have an inkling that something will terastelize, but who know when that's gonna happen, since it could be anyone pulling that shit. And even if it's a pokemon that looks to be a more dedicated tera user like roaring moon, there's like 3 different types it can turn into that have different checks and counters.
If I click focus blast, that's between me and god. I put that on my pokemon knowing I would miss it more often than not. Terastelization turns match ups into a total crapshoot because the opponent might just say "fuck you I win now".
Sorry if this is totally incoherent I'm not great at writing my thoughts down.
