Confirming as NAAA idk
s/o to stresh's excellent mglo arcanine team
I will be voting ban on Noivern because of its ability to win games almost off of team preview. It's the ability to break through so many checks and pivot out to another mon is very valuable to its team and its offensive potential makes it almost necessary to be running something like elecvally, rockvally or nihilego. As Think mentioned in the OP, the vally's have trouble dealing with other special attackers, despite being one of noivern's best counters. In my opinion, that's a sign of an unhealthy mon. It mandates a defensive answer and that answer cannot always deal with other high-powered special attackers.
In this thread, the main AAA thread and the OM discord, I've seen some discussion about other threats such as genesect, blacephalon, and weavile. I'll give my opinions on each of them here.
Genesect: I've seen arguments saying that genesect can simply autowin against an unprepared team. I have to disagree with that statement because genesect doesn't become a game-winning threat until it gets at least 1 shift gear off, which can be difficult because of faster mons coming in to threaten it as well as, depending on the set, defensive mons walling it easily. However, I think with noivern, (hopefully) leaving the tier, genesect may become more of an issue due to losing some of its offensive counterplay. I would be interested in a suspect test to see how it fares if noivern is banned but at the moment I don't think it is banworthy.
Blacephalon: As Think and QT mentioned in their posts in the AAA thread, blacephalon is incredibly powerful and surprisingly durable because of its use of magic guard. However, it is not without its weaknesses. If it is not carrying psyshock, it gets blocked relatively easily by blissey and nihilego. In terms of offensive counterplay, it is OHKO'd by a +2 max attack horn leech from tapu bulu.
Weavile: This is honestly one of the strongest mons in AAA, especially considering its ability to run multiple sets. In the AAACCAT, I believe it used band technician beat up, it can use mglo which is the best set in my opinion, and I'm sure there are other sets. However, it has some pretty good counters such as tapu fini, which is very common, body press skarm, and some corviknights depending on the set of the corv and the weavile.
Sorry for the wall of text and thanks for reading :)