I feel like there's a point that yourlibrarian didn't quite hit, which is: on tumblr there IS a social network culture, and people are friends there (somehow? IDK, I've seen it happen), but that doesn't seem to lead to commenting in the way that being on someone's flist on LJ did. So both posts are true to some extent.

But I do find basically being social on discord and drumming up excitement for my fic does lead to more comments sometimes, at least.