Imo. This is the opposite of having a too big of a community. I think this is just a disadvantage of federation that we will eventually have to live with. The opposite is a bigger problem in my opinion, where one entity controls too much of the power.
What we really need is a better system, be it an app or chrome extension where it makes it easier for us to manage these instances version of their communities.
I don't know what that looks like but the answer isn't difficult to come up with because for the most part, all the lemmies will function the same as each other.
This is actually a very compelling OSS project to make. A Lemmy manager like rss readers of past.
I am working on a multi lemmy manager that Id love to get some alpha testers to.