The main point is being able to still access all of the communities if your admin goes rogue (similar to what Reddit is doing). That's possible on Lemmy, you export / import your settings and you're set.

Keep the same username, add a link to your new and old profiles and the bio, and you just moved instances. You may have lost your comments history, but there is no karma anyway, so why care? And it's still accessible on your old account.