A good administrator, some good moderators, and the ability to create more instances, can solve that situation. The third one is easy, the other two...

That's the nature of entropy in any system, especially one where anyone can freely engage with it. I think it should be recognized that anything good will inevitably change, and by being aware of it, we can take steps to slow down the inevitable descent into chaos.

If anything, I do think the fediverse itself is a good set-up for preventing the sort of issues that Reddit eventually faced. It's almost like the internet itself. There's no centralization, only various participating end-points sharing and receiving data.