> The production of one has huge economies of scale, whereas a song doesn't.

Actually, now that we're digital, the economies of scale of music are similar to software, in that they are massive (and Spotify is a key enabler of that).

> It seems weird to me that your pro-market ideology leads you to support what (to me) seems to be more or less wage-fixing for a labor supplier (musicians)

Musicians have been largely entrepreneurial for centuries. The advent of physical media and distribution control enabled them to form these cartels, and extract rents to enable luxurious "rockstar" lifestyles for a select few. There is now far more opportunity for success and distribution without labels than there has been since they started.