The real point here is that this kind of behaviour is one of things that made Reddit fucking awful and I’d hate to see it flourish here in the fediverse.
Too late, I’m afraid, it already does.
No moderation without representation. IOW: mods should be democratically elected.
Mod elections should be annual and no mod should enjoy that status for life.
There should be a mechanism for inducing a ‘no confidence’ mode election at any time otherwise the communities are likely to splinter into “real_” communities just as they did on Reddit which no community in the fediverse can currently afford.
How do you enforce this? You would need the admin’s cooperation. What if the instance admin is also the mod? If someone starts a community, is it fair to take it away from them, if you don’t agree with their moderation?
There really isn’t any way to prevent all this, it would have to be built into the platform itself and it’s too late to do that now. Furthermore, there are very few communities large enough for people to even want to vote for mods.