This isn't a problem, but a feature. Yes, anyone can download the art, but none of them can provide a proof of ownership of the art except the current owner. Anyone who gives me this article and tells me NFTs are useless is benighted the least.

It's like telling me they own BTC without providing me a valid signature. Okay, you can enjoy looking at the address, but you don't have the rights to move the BTC. When you transact BTC, you do exactly the same thing; you transfer the rights of those BTC. The sign that says it's not yours anymore.