You are right, the 'at' paradigm is present elsewhere, and it is always connected to the fact that the user is included, with his data, in that domain.tld system.
But Nostr is decentralized, the user identity and data are disconnected from the NIP-05 domain, this is just a proxy to the npub and some additional informations. Actually, I can have more NIP-05 too.
I don't know, I understand we are exiting a comfort zone, but I think it's worth thinking about now.