The problem: when a new user who is unfamiliar with the fediverse visits join-lemmy.org, they will likely be turned off when they see how few users are on each server. This is because many people will assume that having a low number of users on your server means that you'll have a low number of users to interact with. (This is what I assumed when I first discovered Lemmy.)
The solution: instead of showing the number of users on each server, we should instead show information that feels more intuitive to new users and doesn't mislead people into assuming the user count is more important than it actually is.
I think it would be a good idea to show the date that the server was founded, and show the server's network traffic in terms of Low/Moderate/High. I think this would make the prospect of joining a server much more appealing to new members, and it would also help them understand that it's actually a good thing to join a server with fewer users, not a bad thing.
Here's my quick mockup of what it could look like. (I made up random dates but you get the idea):
I also like the way that PixelFed explains the federated system: https://pixelfed.org/how-to-join