So what I am trying to say (but it's hard) is that you are arguing against community relays and making all kinds of assumptions about how it will work.  And now I got suckered into doing the same 😂 I could talk about all the ways nip72 is broken but I won't.  I will simply say, it's not clearly defined what community relays or communities are and it's going to take a client or a nip to enter that frontier of unbuilt functionality.

Clients will eventually move away from the blaster model of all notes on all relays.  This is already a terrible experience and centralizing force that is killing smaller relays.  We already know how to find other npubs via gossip, and we will need a similar way to discover communities otherwise we are all just missing our replies because the messages are on relays that we aren't connected to.  And along those same lines, some relays will not want to carry certain topics that is their choice.

The closest thing I've seen to making progress in this realm lately is this nip: https://github.com/nostr-protocol/nips/pull/566#issuecomment-1806961991