A lot of duplicate communities arose organically though, to fulfill a new niche. Sometimes it was stuff like actual lesbians finding that /r/lesbians was a porn sub, so they made /r/actuallesbians.

I can't think of any examples right now, but there are also definitely cases I've seen there the offshoot variations arose organically, diverging from the main community.

I'm not disagreeing with you, just wanted to highlight that many of the variations on Reddit weren't the same, but smaller, but subtly different and thus catering to different communities (which may have overlap with the original). I worry that this kind of "speciation" won't happen if the fragmentation remains too great.

A key aspect is that you could generally tell the difference between the offshoot subs by the name, which is harder with this instance model. For example, I don't know what the deal is with /r/AITAH, but it's fairly clear that it's an offshoot from the main Am I The Asshole (AITA), so I can assume there was some beef. There's also cases where a mass exodus from a sub is justified and the "primary" sub (most active users) is not the "original" sub. It's just harder to tell these things from the name on Lemmy