Implementation details of an app are what make the difference between "ease of use" or not by end users. That's not a 'protocol issue'. I've implemented both a Fediverse and a Nostr implementation from scratch before, and had them running. I ended up abandoning both for separate reasons. I speak from experience when I say ActivityPub is a nightmare to implement and Nostr is easy.

What Nostr got right is that the core of the system needs to be very simple and be ALL that's REQUIRED to join the network, and with Nostr you're just signing a JSON object with your crypto key and you're DONE. And Nostr objects can live "anywhere" too because the user identity is in no way attached to a DNS name. With ActPub your lovely "Admin" (who might hate you and your politics) becomes your god, because once you build up a following on a specific name, you must bow down to your new god, because they are the TRUE owners of your name.