YouTube is an on demand stream. It would be comparable to recording a pay per view movie that you purchased. Is that legal? (The question isn't rhetorical, but I seriously doubt it.)
That's a kind of tech adaption of the streaming/playback mode (and I've done it a ton on previous laptops)
Right, this is the precise problem, and it has to be solved - not by a free-for-all but with proper equitabl copywrite laws.
As matters stand, it's only going to get worse. Say we assume that if somehow both YouTube downloads are made much more difficult to crack AND no downloaders are available, then viewers and downloaders will then use newer tech that's even easier to use to record the videos. With new hi-resonution 4k cameras becoming commonly available, they'll be able to record stuff with still-excellent resolution by just photographing the monitor.
Of course, that still won't deter the RIAA, I can see them trying to ban cardboard covers and jigs that hold cameras and monitors accurately in alignment.