This has been a thing for a while now, hasn't it? I remember trying to watch the Noseferatu trailer a few months ago and seeing how shit it looked. Tried to up the quality only to see that it was paywalled
I mean, that's an advertisement. I feel like if you're going to watch an ad, that the company trying to sell the product should find a way to have the ad in full quality themselves.
It looks like the official website does use YouTube, though.
Personal experience, but I feel like it has. Especially on videos with a lot of still frames like 3blue1brown, you can see the still images become slightly better quality after all the animations stopped. I noticed a few months ago and saw 1080p premium as an option.