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.
A recent Piefed update allows to follow Mastodon accounts: https://piefed.zip/c/piefed_meta@piefed.social/p/1736809/piefed-v1-7-11-is-released-finding-and-adding-people-to-follow-posts-from-rss-feeds-and-mo