No because Spotify pay the rightsholders who may or may not be the artist.

You're missing the point. Let's say Spotify pays rightholders 20% of gross revenue for streaming. Then they take another 40% of the gross revenue and pay the major labels for advertising, marketing... whatever. That's hollywood accounting-- it's not streaming revenue so they don't have to report it. Ever notice the labels don't complain that the streaming rates are so notoriously low? Why don't BMG/UMG/WMG just band together and demand an increase in streaming revenue? Because they WANT to keep it low so they make the real money on non-streaming revenue that doesn't go to rightsholders. Maintaining control is the issue and that's why they forced Spotify to make people work through their "partners"