I think the premium thing is a channel option. Some channels consistently have it, some don’t.

Regular YouTube 1080p is bad and feels like 720p. The encoding on videos with “Premium 1080p” is catastrophic. It’s significantly worse than decently encoded 480p. Creators will put a lot of time and effort in their lighting and camera gear, then the compression artifacting makes the video feel like watching a porn bootleg on a shady site. I guess there must be a strong financial incentive to nuke their video quality this way.