I like the idea of blocking or unblocking whole instances.
That said, I agree with commenter above you: I don't see an issue with large instances. I value having a bunch of different options, and we do have a bunch of different options. Running an instance yourself requires a fair amount of work, so I'm glad to have others willing to take it on.
If anything, on the subject of control, I like the model of social.coop over on mastodon where users can vote on direction and volunteer. It's also more formally funded by user donation (you have to set up a contribution to create an account) vs instances which are funded by donation but it's kind of whoever decides to chip in.