so, hot take, but I think the answer is "other human curators" and I think it can work even though it sounds like an ouroboros type impossible system.
the trick is that the curation focus of one curator needs to source from curators with slightly different yet often (for various definitions of often) overlapping foci, and at least some curators need to be sourcing from direct sources - the people making the thing that needs discovering.
alcinnz