This isn't the only time I left a critique of ActivityPub-as-Deployed as opposed to ActivityPub-as-it-could-be: see also OCapPub, which critiques the anti-abuse tools of AP as inadequate and leading to "the nation-state'ification of the fediverse" https://gitlab.com/spritely/ocappub/blob/master/README.org
Oh, and ocaps!!!
ActivityPub left giant holes in the spec around two things which sound the same but which are not the same: Authentication and Authorization
Trying to mix these two, you accidentally get ACLs, and then you get confused deputies and ambient authority, plagues of the security world