But then you're relying on the IPFS version to accurately say which Youtube video URL it is equivalent to. I could upload any number of videos claiming to be the same as your video, right?
True. Maybe that can be solved with an oracle[1] that runs the command “yt-dlp <url> -o - | sha256sum”. So every file you upload must be identical to the YouTube video at the same link.
1: https://ethereum.org/en/developers/docs/oracles/