Nuh on Nostr: Yes but you are assuming that the community keypair will never be lost or made ...

Yes but you are assuming that the community keypair will never be lost or made vulnerable or compromised or the community wants to fire the admin and transfer custody entirely to another admin... The last one is probably easier to do by moving to another community, but the previous concerns are valid.

They can't be fixed without a Blockchain though. Or a centralized authority... Hence DNS.

So you could have communities identified by a domain that points to a nostr Keypair in a TXT record... Which would be easy to upgrade to Blockchain based DNS like ".mns.alt" once/if it is ready