You might be right about being able to do almost anything whatever the instance you choose, as long as you already figured it all out, but having an account at a lemmy server, and two at two different mastodon servers, I do have the feeling that the presence on any of them is a different experience.
Don't forget that what most people's experience on the fediverse comes probably via mastodon and that they start by getting most of their content via home and local feeds. Federated comes third, i guess.
I am still struggling to find content on some of my preferred topics...