@trwnh nice writeup! Just glancing, so without getting into detail, I think I agree.
This is perhaps my own bias in all of this, but it's interesting that one of the most-consistent aspect of Fedi implementations is their reliance on Webfinger.
I worked on that part because I didn't think the data format stuff really mattered that much, and at worst was going to be stifling. It was excluded from AP for political, http fundamentalist reasons, but [imho] is essential to the networks functioning.
@trwnh linking, which as you point out is key – to people – depends on regular people being able to share their names. I learned a long time ago that most people aren't good at groking the HTTP part of links, because the structure of links is actually really complex. When you mention xmpp and email, the identifier is the thing that makes both of those networks work.
For me, "fedi" or "AP" or the social web or whatever we want to call it has always been about making personal identity linkable.