It consistently plays thing which are clearly not songs in it's auto playlists, it has no consistent normalization or quality, and makes finding albums more difficult than it needs to be.
It is an algorithm slapped over youtube rather than a music service.
GPM and YTM are identical subscriptions and always have been for as long as I can remember, if not forever, save for that short time when YouTube Red was inexplicably a few dollars more per month compared to GPM.
I actually switched to YT Music a year ago as I preferred the UX. But it's indeed subjective.