I think...to me I would object to Spotify pushing their house-made music using their suggestion features (Discover Weekly, the horrid "Smart" Shuffle feature) - but them making playlists with their house music and offering them to users feels fine. I think that is how I would slice it when thinking about the Amazon example (that IS anti-competitive and monopolistic and should be illegal imo).
Edit: I have not looked into market share deeply but others in this thread have said the Spotify market share is ~31%, which does not seem obviously overwhelming to me.
That's a perfectly reasonable stance. I would point out that historically, 30% is an extremely high market share in any industry, and represents a high degree of consolidation (esp given that Apple probably has similar share, so the two of them control the market).
That is more a result of how insanely the US structures intellectual property rights. The problem is that one company having that much marketshare usually creates a defacto private regulator of the industry, which goes against the whole notion of people being governed based on consent.
Edit: I have not looked into market share deeply but others in this thread have said the Spotify market share is ~31%, which does not seem obviously overwhelming to me.