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?
I see it as a good thing - like you say, people can find the community that suits them, just as fans of a football side can join one (non-Reddit/Lemmy) forum or another (or both).
Likely one or two communities on any given topic will become the dominant ones over time, but for now I think it’s good that there’s a chance to kind of start over with communities following their own principles and ideas.
What might be good would be if communities of the same topic were to agree to crosslink to each other in their sidebars (much as the sfwporn network did on Reddit).
I think keeping them as separate communities with separate mods is a good thing though, it lets the subscribers decide if a community is what they want, without it being the only game in town.