The only thing worth a YouTube premium subscription is probably the higher bitrate formats if you download/archive all the videos you care about. Latest version of yt-dlp gives you access to those (except the highest audio quality format, I think it was 256kbps AAC), but this will probably be patched sooner rather than later.
That’s pretty much implied in my message with the 256 kbps AAC which I believe is what youtube music is using (format id 141).
Downloads and background playback on mobile is already possible,
Whatever I don’t even care what you guys think anyway, I gave my opinion, you don’t like it, that’s fine.