With reddit, subs would get big and shitty, then you'd see something like,"Hey, join us over at . It's like this sub, but with(out) ". And that spinoff had enough momentum from the start to keep going.

Except that's not what happened. What you're describing was very rare. The vast majority of the time, terrible subs with terrible mods or user bases stayed entrenched, alternatives never took off. The main sub would always get recommended, it was the one Google would show, it was the one that hit the front page, the small subs just never got that exposure and most dwindled.

It was a big issue people didn't talk about much, and I like that Lemmy isn't worrying about consolidating.