IMHO, selecting an instance is definitely the biggest user experience problem Lemmy has at the moment. New users who are unfamiliar with the platform are going to pick the biggest instances, and that's going to create performance problems.
We'll need to prioritize work on instance browsing. Lemmy has outgrown the experience over at join-lemmy.org. If I could wave a magic wand, instance browsing and onboarding would have a way to show instance capacity / performance, a way to categorize and filter instances, and a way to recommend instances based upon interests. That would probably help to spread people out more evenly.