This is patently false. YTM has a library of tracks and albums that is equivalent to spotify or Google play music. On your phone it's a totally separate app from youtube. In addition to the spotify-esque library of music it can also tap into yt, which has a longer tail of indie stuff.
> ... player is buggy ...
I don't experience exceptional buginess in the player, although there are things that annoy me (same with spotify). However you are moving the goalposts, I thought this was a rant about deleting data? Now it just sounds like a rant about Google changing ux.
* ... merging likes ...
I also did not experience this problem but they did screw up the order of my likes which was very annoying. This complaint is still off topic though.