That's a good take, and maybe at some point I'll do just that - who knows! For now (and maybe people will tell me I am holding it wrong), I want my account, which is my identity, to be in my control, that's the main reason for self-hosting. If Mastodon supported hosting custom domains in the same manner that, say, GitHub Pages does, I probably wouldn't have bothered with my own instance.
And I don't see how that prevents me from lurking on other instances local feeds, picking out people I'm interested in and following them so that they appear in my own feed. It's true that I don't really know which instances I am interested in right now, I know a fair few folks I am following on Twitter are @hachyderm.io or @fosstodon.org.