It's a big problem all across the fediverse. New users have no idea which instance to join. In the absence of any way to differentiate between instances, they go with the most popular one, or the one they've heard of the most, or the one that sounds vaguely official or "vanilla". Lemmy.world is the obvious choice for these users.
This leads to the biggest server becoming a runaway train, which is bad for diversity and also bad for the admins because it makes it harder to manage the load. It's the same thing with mastodon.social.
I would encourage users to avoid the biggest instance as a rule, no matter which service they are signing up for. Ideally, avoid the top three or five. That will naturally lead to a healthier balance.
The problem is, there aren't a lot of "general purpose" Lemmy instances. Someone following my advice, who doesn't know better, might find themselves on hexbear, dbzer0, or lemmygrad. These are bad choices for a new user who expects something more or less equivalent to major centralized sites.