The part that still baffles me is that if you did that, the NFT community would just say "oh well that's not the REAL owner!" and pretend you don't exist

Similarly if you "stole" the blockchain receipt of an actual NFT, therefore gaining "ownership" of it, the NFT community would simply pretend the person you stole it from was still the "real" owner, despite having zero "verifiable" status to it, beyond having possibly tweeted it before you did

I have to use a lot of quotes because even in a hypothetical there's so many variables that applying real world properties to just make my head hurt

You can't steal a blockchain receipt. Here's a challenge for you: go right click a CryptoPunk and save it, or use this NFTBay to torrent the JPEG yourself. Then try and sell it.

And in a day or two, you could find the most expensive old Dutch master sold at Sotheby's and have a perfect digital replication.

Nobody would stop you from hanging it out up in your living room, or even announcing to everyone on social media that it's the original and you're the owner. Nobody would need to, because everyone in the art collecting community would recognize this as super cringe.

People purchase art for social status. What you're describing is the opposite of social status.

I still don't see how a digital copy can have the same brush texture as those of Dutch masters