Many of the subs I spent a lot of time posting on are completely dead, bar maybe a few people that contribute 90% of all posts and comments. Others simply don't exist, and given that they were quite niche (local subs, anime subs) there's absolutely no way that they'll ever get noticed on Lemmy if something like pro wrestling has next to no posts/comments.

IMO, the only way this will improve is a combined effort from Lemmy instances to highlight great communities, and to drive people towards ones that are growing.