No it’s not. Anyone could have put an artwork on the blockchain, even if it’s not theirs. Just because Alice uploaded an artwork doesn’t prove rule out the possibility that Bob was the creator.
Blockchains cannot link to the physical world while keeping their properties of ‘proofs’, yet so many projects seem to ignore this inconvenient fact.
Conversely, it is the previously unknown things that would most need some confirmation of authorship, yet here the blockchain concept fails again!
There really is a market for unique stuff, even useless unique stuff. See Upland, Decentraland, etc., where people are buying virtual real estate. In Decentraland (which is totally centralized) you can at least log into a virtual world and put something on your land. Upland skips that step. You just get tradeable certificates which supposedly represent real-world locations to which you have no rights.
Sure, they have some hard coded authority for which NFTs get included in their marketplace, but people are free to switch that up on their own instances.
Sure, there are ways in which it could be more decentralized, but it's a hell of a lot more decentralized than anything else like it. I'm doubtful that any further decentralization would provide additional value to the ecosystem. If the devs go crazy though, it would take maybe a day for a handful of people to fork it and correct any leadership issues with the project. So far though, the leadership has been fine IMO.
Beeple's Christies auction will be very interesting.