So you are saying Mastodon won’t take off because people need to choose a server but also because having a “default” where majority will ptobably end up is bad - but this is literally the solution to the problem you mentioned
It’s the solution on the user experience side, but not the backend/server side. For both infrastructure and idealogical reasons. These two things don’t have to be the same.
Disney parks wants park visitors to feel like their exploring, but design in such a way that thepy don’t actually stray that far from the preferred paths. Also they have clear sign posting.
There’s no reason the fediverse can’t design the opposite. Helping users into feeling like there’s a set path, and that they’re doing the right thing, while subtly encouraging exploration.
It’s just the opposite of where all talent and techniques of internet software design are right now, so it’s going to take some work.
Edit: Most people don’t jump into a hedge to get off the main road, they find a small, unplanned trail or desire path, then learn to navigate the jungle when that path ends.