I used to use Poweramp few years back, then moved to more "streaming" kind of app, but it looks like offline playing is the way to go.. I briefly tried rimusic but it had all sorts of issues with offline content and streaming was disconnecting every so often.. Guess it was not the fault of the app directly, rather it was getting blocked in he background..
also spotify is okayish assuming one is accepting the profiling.. but you can limit how much it can gather, and you could host it on something like a raspi and connect from phone to stream. I personally dislike yt music..