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.