Spotify pays out 70% of revenue they receive to owners of the music, BandCamp 75%, SoundCloud 80%. Could be slightly better, but it's not outrageous.
The real problems for artists are:
a) they are not the owners of the music, their record label takes most of it, and the rest is split between the artists, songwriters, producers, etc.
b) bad deals with (but good for) the customers - ~10/month for unlimited music too good value