Nostr doesn't even have the decoupling afforded by what we typically think of when we think of federated networks (email, activitypub, matrix). If you and another party aren't using the same relay, there is 0 way for you to interact. It assumes either you pre-agree on a relay (sticky defaults encouraging centralization) or shotgun messages to many relays (economies of scale encourgaing centralization). The protocol explicitly forbids relays from forwarding to each other.

Nostr is a very simple protocol that could have been invented in essence in 1995. There's a reason it wasn't invented until recently, because it's difficult to build robust protocols with good guarantees about discoverability and reliability with a foundation that is as limited as it is.