If I might make a suggestion, assuming it wouldn't cause more of a moderation nightmare: Maintain a list of soft banned topics that get relegated to a weekly "containment" thread. Complaints about explicitly stated instance wide rules get routed there. People have their space to complain but it keeps things cleaner. It also still allows this place to serve as kind of a watch for abuse. Just because it's a clearly stated instance wide rule, or that anyone can pick up and go somewhere else on the fediverse, doesn't necessarily mean it's not being abused.
Either way, I despise the idea of deleting the previous threads. There's nothing illegal and people should be able to draw their own conclusions about those shitshows. I think the previous threads should be locked to prevent any further comments requiring mod work, but left up. They are important context to this whole mess in case it flares up again. Really sucks coming into something late and being attacked for asking questions that are only obvious if you're already up to date, that come across as attacks to people already in it, but you have no way of knowing any better about.
I also have some concerns about this comm if certain topics start becoming forbidden. It limits the ability of this space to allow the community to pass judgement on and discuss mod/admin actions. But not limiting could end up with this com just devolving into a complaint quarantine for leapords ate my face "contestants".
Tl;dr- don't ban topic (maybe a weekly quaratine thread for certain topics), lock old threads and leave up