We already know that centralized social media has a huge problem with bubbles right now, and this problem is a direct result of companies trying to monetize the users and keep them engaged.
On the other hand, federation is a self organizing system where the networks grow completely organically. This is much closer to how humans organize and interact offline. Everybody can run an instance, and they can choose how they moderate it and whom they federate with. There's no single company deciding what's right or wrong for everybody. There are going to be all kinds of extreme bubbles, as well as moderate ones, and everything in between.