Until last month, kids could not use YTM. With the family plan, this was basically a DOS for years (or setup new kids accounts and lie about their age).
IMO, GPM's recommendations were much better.
We kept the family plan because of YTP and my wife and I still had access to music.
The lack of kids support is very true. The free tier also was quite trash for a long time, and the lack of desktop casting. Most of these have been since fixed though and at this point I would say YTM has feature parity.
Recommendation is always hard to discuss as it's very subjective. That being said, YTM has great playlists. It automatically clusters your music into 7 playlists which is describes with 4-5 artist names. There's discovery, replay and new release mixes which are great too.
Overall, I agree GPM got shut down way too soon, but at this point YTM has made a lot of progress vs what it was 2 years ago.
Wasn't that just moved to Google Podcasts? (Although, something like PocketCasts IMO is a better service.)