It used to be the case that apps couldn't access the music managed by iTunes, that hasn't been the case for a while now though, apps can get access to that music now.

I expect people listening to their own music, as opposed to streaming, is very much a shrinking market.

I use the Apple Music app. It isn't perfect, but now it actually has now playing playlist management it is more usable (and empeg-y) than it used to be.