Which turns out to be pretty useful and maybe have value.
To know if this piece of paper was actually touched by the author, we still need verification outside of the blockchain.
It’s not obvious to me that all this has any value. “The author probably blessed a number” certainly doesn’t have the emotional connection of an actual physical signature, for example.
In a way NFTs seem to resemble the medieval church practice of selling indulgences. If you believe in the authority of those mass-produced blessed pieces of paper, they have value.
It's also trivial for any author to change that message to a new hash so they can sell their NFT's again. Or the service where that message was posted might disappear, so you can no longer view the message and therefore nobody knows that the NFT is "authentic". So you basically get the same problem as any central authority of trust. In this case you trust the message board the author posts on, and you trust the author, and you have to also trust the service hosting whatever art the NFT points to. If you trust those then why not just trust a regular exchange instead?