If all the clients used the outbox model, I think 2 relays is about right. My webpage is on only on one server and that has been fine - it is rarely down and nobody has tried to censor it (yet). Why should it be different for my nostr content? All the redundancy in nostr is only prematurely clogging up the relays for very little benefit. We can always scale up and use more relays for more redundancy if we find ourselves under a censorship attack, or whenever relay failures are common, and we can scale down and be less redundant as relays are more reliable.

But given that some clients aren't looking for events in people's declared outboxes (and many people don't declare anything at all), we still have a lot of unnecessary redundancy and even event copying (I think).