You can use an account on all instances but I think the lack of consolidation is the single biggest problem with Lemmy/KBin tbh (the lack of ActivityPub in some of the other Reddit alternatives also doesn't help).

Obviously there's a smaller userbase here, which is fine and expected but can make some communities feel a little empty. Having basically the same community in multiple places across multiple Lemmy and KBin instances makes that issue a lot worse though - ideally communities covering the exact same topic should be automatically consolidated in the way you describe. And ideally on an opt-out basis for the user - so you see the amalgamated page by default and can see the individual ones if wanted.