As far as I can tell from my venture into Mastodon’s feeds, the demographics of that part of Fediverse isn’t that different from what Lemmy has: the same political takes, FOSS stuff, “big corpos bad”, etc.
I wonder, is there anything that Mastodon excels at that Lemmy just doesn’t provide? For example, I noticed that there are game developers and artists posting their stuff on Mastodon. Not many game developers (or any creatives, really) on Lemmy though.
For the commuities/topics I’m interested in Mastodon has a very weird vibe that clashes with the vibe of the communities on Lemmy and sometimes it feels like the Lemmy communities are getting brigaded by Mastodon users. Also Mastodon comments are very “noisy”, every comment needs an @someone to work and every second word is a hashtag. If I check out Mastodon on its own it just seems like a lot of people screaming into the void, but I never understood the appeal of Twitter either.