If you use the outbox model, and your few outbox servers got DDoSed you still have the same result as Mastodon here. It doesn't matter that you have 3 outboxes instead of 1 homeserver... You are either;
1. Using one paid relays which the same as Mastodon server
2. Using multiple free relays that owe you Nothing and have no promises of resilience.
Nostr is not a reliable network it is censorship resistant network, somewhat, so don't shame people for having popular servers, that is user choice and they get things out of it that they consider more valuable than what you get from Nostr.
