I think GP's point (which I agree with) is that the functionality is almost essential. When it's not part of the spec, then you end up with differing off-spec implementations, and again, centralization risk.

This would be like the HTTP protocol not defining `POST`, and leaving it up to servers and clients to implement it based on however it feels like.

I really like the ideals behind Nostr, but I think its implementation and execution could be better.

It would be more analog to HTTP not specing out how CDNs should work, or Usenet not specing out how DejaNews is going to work. It's infrastructure stuff neither the client nor the simple server has to care about.

The Nostr spec covers what matters, cryptographic identities and unique message ids, that make dumb relays that duplicating messages from elsewhere possible (an area where HTTP or Activity Pub fail at).