@davew I think there's a disconnect here.
ActivityPub is built upon objects being dereferenceable through their IDs which are theoretically immutable URLs. Or, I misunderstand what you mean by "LINKING".
Client to server collection addressing of ActivityPub objects is basically fulfilling the same function of RSS with the difference of using JSON as an encapsulation method instead of XML.
Maybe your problem is with specific implementations of C2S - which I'll be the first to admit - in majority, follow the Mastodon lead, and are severely lacking. However the specification itself should cover all that RSS/Atom offer and more.