Spotify has very low margins so it's hard to say 30% isn't fair. Any lower they'd have trouble paying their costs. Streaming in general helped the music industry revenue grow. You can say Spotify might be bad at business for not making much money on a 30% cut, but overall they seem to be serving decent value for money to the copyright holders and customers. Before streaming, the overhead was a lot higher, with the retail distribution chain taking a comparable cut.