True! Outbox model works better for known unknowns. Unknown unknowns become harder, but if you request a list of notes signed by a given npub and verify the sig of each then that’s still a parameter you can use to avoid being spammed by the malicious relay.

You can at least retrieve tons of notes from everyone you follow that you might not have seen otherwise, like the hello world experiment from @fiatjaf 

If the relay model and Negentropy in the client, you could even send the list of note hashes you have for that npub so the relay would intelligently respond with only the notes you’re missing, completing their profile. 

 Outbox model + Negentropy in the client = Incredible syncing — described above👆 

 REQ filters are not ideal, and negentropy-style syncing might be more efficient in some contexts. But REQ filters do pretty good. I can get all your notes over a time period, and if new notes flow in during that same time period (belatedly) I generally will miss them.  But with some time overlap, hopefully I won't miss any notes that were put there in a timely fashion, which the outbox model generally will do.