@mike I think the big algorithm-driven silo sites have us conditioned to place too much importance on discoverability. Although federated platforms have been criticized for not having the discoverability of big central services I have not had any problem finding and following people I am interested in from a self hosted instance without the use of relays.
Activitypub seems like the evolution of Atom/RSS by bringing in more interactivity, which enables sufficient organic discoverability...