I also think it's BS but not because of what the NFT contains or not. The signature is already intrinsically part of the NFT since you can see what wallet minte

I also think it's BS but not because of what the NFT contains or not. The signature is already intrinsically part of the NFT since you can see what wallet minted it on the blockchain. When you mint an NFT you sign the transaction on the blockchain with your wallet. As you say what actually matters is proof that the signing party is the real one. And this is where the social contract matters. What gives it value is that artist X says they own wallet Y and that you can see that NFT Z was minted by wallet Y. It's just a fugazi but it can't be fixed by adding stuff to the NFT object.