"ActivityPub and ATProto break #siloing in different ways. #ActivityPub is built around URLs and can "socialise" more or less anything on the Web, which is great, but they don't touch the underlying substrate—either you run your own server or you…are at the mercy of an admin. #ATProto, on its side, provides a good initial foundation for an extensible #PDS designed around user agency and credible exit.
…you can be guaranteed to be able to take your content elsewhere." https://berjon.com/ap-at/