Having tried all three, its a stark difference in how much more social Lemmy is comparatively. Its not even close. Almost all posts I've encountered on lemmy have interaction; whereas, more often than not, posts on the other two platforms have no interaction. Wonder what the driving factor is behind this difference?
Lemmy is discussion focused, the bulk of content is the comments guided by posts. Mastadon/nostr are about microblogging, the posts are the focus of content, not the comments.