Lessons from Spotify
The authors central point seems to be that Spoitify is at the mercy of the record labels. Because the labels have the music. And that Spotify can't cut them out because they don't have enough users to attract artists:    Notice how little power Spotify and Apple Music
    have; neither has a sufficient user base to
    attract suppliers (artists)

But he does not explain his reasoning behind it. How big is their user base? Why is that not big enough? And how big would it have to be to attract artists?