Where the analogy falls apart though for me at least, is that emails are always private, i.e. there's no public feed (shared mailboxes excepted, I guess)
So if I come across a toot(?) by @
[email protected] and then later in the day come across another toot by @
[email protected], I have to remember which one is which. In most cases that won't be an issue I expect, but if it takes off to the point that celebs and customer service types are frequenting it, suddenly it becomes a breeding ground for people to impersonate other people and you've got two @elonmusk's at different servers, both with identical profiles and you just have to hope that you're interacting with the one that ISN'T a scammer.
Now yeah, you could level similar criticisms against all networks, including Twitter, but the lack of a centralised username database is just utter bonkers to me for this reason.
And yeah, the onboarding process is shash. It just reeks of something that's been designed by geeks, without any thought being spared for the "common folk" that might end up using it.