It's important to be able to filter the abuse. If zap-endorsements are easy to fake then I don't think they'd work for the seed at scale.
With nip05 that's more or less trivial - you see a bunch of spammers all from the same domain, and you blacklist it. From experience, even some root zones will have to be blacklisted. How things evolve around zaps is unclear for me now, so we'll see.