i have a layman’s understanding of AT Proto, but it seems to compartmentalize between different parts of the service. Front ends, databases, and backends can be hosted separately and amalgamate into one, in the abstract.
Practically, however, AT Proto allows account portability, wherein users can swap what instance they use as a frontend on a whim, even if their home instance is down. Usernames are domains instance of username@domain, that are verified by the DNS. But AT Proto seems a lot less flexible than ActivityPub. We’ll have to see when federation is live, but I’m not sure it really suits anything beyond (micro)blogging.
oopsies