> If they'd just give me a feature that gives continuity of play between devices I'd pay the full monthly price without blinking.
What specifically are you looking for? e.g. was watching a video on my computer, powered that off, opened youtube on my phone and the video I was watching was most recent thing in youtube history there with my position in the video tracked. Similarly I can use my phone or laptop to control Youtube on my TV. Seems like what you're looking for is already mostly here.
(I've been a Youtube Premium subscriber for the last year or so thus far).