I agree with your analysis, I just wanted to point out that this is effectively a regressive taxation. In this instance, Spotify is the state and from it's perspective, it makes sense to tax the pop stars less (as a %-age of income) than some tiny alt-nu-grunge-garage-under-over-in-out rock-jazz-house band. That's what maximizes Spotify's tax revenue. But it's still a regressive tax. The richer you are (in the Spotify ecosystem) the less of your earnings you have to give up. Whether this is fair or unfair is debatable - I suppose in a pure market economy, whatever the market agrees on is fair. But there's a massive disparity in negotiating power, which means that the small artists are naturally disadvantaged. Big popstars have a huge concentrated negotiating power. Small artists do not. It is thus less likely that they'll be able to negotiate a "fair" revenue model, whatever that might mean.

Again, fairness is debatable. As a society, we decided that regressive taxation is unfair, because rich people can proportionally bear much higher taxes than poor people without impacting their lifestyle. I'm not going to go into the realities of rich people ending up paying a much lower effective tax rate due to being able to afford to optimize their taxes.