A lot of disingenuous Lemmy users in that thread pretending that picking a server is more confusing than filing your taxes. I think join-lemmy should probably hot-list like 6 or 7 servers instead of making you choose via a primary interest, since you can migrate your account later anyway. But I am personally not tech oriented and managed to make an account and find an app without an issue.
The goal was never to convince people who don't know how email works to join, it's to convince an average reddit user to join.
Unless something has changed, migrating your account is more like copy/pasting config on a new account. Your post history etc however does not come with it. If that's something that matters to you then picking the "right" server matters a little bit.
For example lemmy.world has defederated from a bunch of instances (https://lemmy.world/instances)
Creating your account there means you're missing some of the full experience of Lemmy, for better or for worse.
A smaller instance may federate more content, but may run slower or worst case stop working entirely if the admin abandons it.
I just used a handful of different servers over the course of a few weeks to see which was my ideal server.
it's confusing from the perspective of choice paralysis, ultimately you can just make a new account and move to another instance if you really don't like the one you're on.