Relays shouldn't have to know about other relays. They just worry about themselves and their interface to clients. It's the clients who are deciding which relays to connect to and how to fetch data. Maybe I'm misunderstanding your point though...

Maybe I made a mistake. As I recall, nostr.band and nostr.wine have a service that helps link users of their relay to broadcast their messages to other relays. If no matter the size of the relay complies with a certain protocol, as long as the relay service is operating, it can automatically relay to each other, so that the error of the large relay can be avoided. This is optional, of course, because there are many people who want to run their own small relay.