I understand concerns about fragmentation, but recently, I have been more and more in favour of "why not both" as an approach. Basically: One de-facto "central" community, and many local communities. Main reason being, that this will help the Fediverse grow without losing it's "soul" so to speak. Where - hopefully eventually - there will be those central communities with a reddit-like experience for the topic, and then also local ones, where smaller communities around the topic, without the traps of large, "mainstream" communites, can form.
I see where you come from, but splitting a tiny group of posters across different communities doesn't seem the best approach at the moment. Also, it forces people to follow the three communities to see all the discussion happening, that's an issue that's regularly brought up by people criticizing Lemmy