> If an external source - say the Twitter account of an artist - can authenticate that the holder of the NFT is who the creator of the art work wants to be recognized as the owner, then social consensus will lead to widespread value assignment to that NFT.
In other words, you don't need the blockchain because the actual value comes from a different system. The only thing it's adding is overhead and unreliability.
It fails to establish that this is unique to a blockchain: we do, after all, have decades of experience building distributed applications and it’s not like banks haven’t issued loans before and the hypothetical benefits have to be weighed against the added costs of relying a very slow, expensive database with no mechanism to correct bugs or fraud.
"makes that asset accessible to a large number of autonomous on-chain markets, like dApps which allow a person to take out self-executing loans that use the NFT as collateral"
What market undergridded by banks provides these features.
The blockchain provides extremely high assurances of up-time and immutability in its protocol rules - which assures accessibility and protection from third party interference. This is ideal as a digital asset registry.
In other words, you don't need the blockchain because the actual value comes from a different system. The only thing it's adding is overhead and unreliability.