I had my entire music collection stored on Google Play Music for a time, at one point being my only backup. When I tried to export my music collection, I discovered that not only were the file names and folder structures completely messed up, but I would sometimes get lower bitrate version of the songs or songs with "clean" lyrics - which I know for a fact wasn't what I had originally uploaded. I refuse to use music…
I don't have the RPi connected to the internet though. I just load my phone with MP3s like the old days, and open up NewPipe[3] when I want to listen to something I don't have stored.
[1] https://www.foobar2000.org/