Look, without agglomeration there is already a strong bias for any topic to have just "one big community" on "one big server" like lemmy.ml. Because why would anyone post anywhere else than the one community with the most users.

That's the same reason everyone is on facebook and reddit. This is a fatal flaw of Lemmy. Just because there are many servers that doesn't resolve the problem of centralization if everyone posts in the same community of the same big server.

And no one will manually subscribe to 1500 "books" communities with 5 user each, even if they existed. The solution is a single view that sees all "books" community by default.