With reddit we mostly had a single subreddit for a given topic, for the sake of the question let’s use gaming. If there were alternative subreddits dedicated to the same topic, they had names that gave that away. Do you think Lemmy will lead to more segmentation, and more information bubbles seeing as we now can have gaming@x and gaming@y without a obvious way to see which community is the “default” one? Will it be a good thing, as you can find a community that suits your preferences better, or will it stifle discussion?
Sure, there will be one community that is the community for a particular subject. For example, there’s no good reason to subscribe to several communities for “Springfield Massachusetts”. The most popular one of going to be the standard.
But maybe different “Politics” communities will have different leanings and contributors that you value for different reasons - and they can each go strong.
The thing is, no single server should have all your subscriptions. You might get news from Beehaw, games from .ml and do a book club through Kbin.
Because no server/instance owns all of it, the federation checks and balances itself. If users are unhappy with mods or administrators, or whatever - there is a choice. They also don’t have to delete the app they use (when apps start rolling out officially. I’m beta testing some).
There is competition for users - and that’s a good thing. It means that user experience will come first.