This is so inherently detectable, though, I'm amazed it worked for so long and that it's still working now. Likely a consequence of offloading as much of YT onto the client side as possible, because if you're doing anything server side how hard is it to require that the ad has at least downloaded before streaming the video?

The Spotify ripper "zotify" has an undetectable "realtime" mode that does basically what OP suggested. Instead of downloading every track as fast as possible, it pretends that it's actually streaming and listening to them. Obviously it takes a lot longer to rip a whole album, but it's a good idea.

I think Spotify ripping isn't big enough that it's actually needed at this point, but it's good that they considered the potential for it.