"specifically restricted function"

I think you are conflating purpose and function here.

I doubt any music has a 'specifically restricted function' for the ones who 'consume' it, whether pop, the old ballads, shanties or whatever. Of course, those who purvey it might or might not have a narrow sense of their own purpose, but somewhere along the way, there is an irreducible impulse that resists single-fold characterization.

Have you seen John Cohen's film 'The End of an Old Song' recently?

Cohen recorded Dillard Chandler saying some very moving things about the place of ballad singing in his community. Cohen's own attempt to distill all that into a few aphorisms had a bit less depth and richness, but still affirmed something about the tenacity of attachment to the old songs.

There's lots of recent stuff about music and the brain (Oliver Sacks, Levitin and so on), but really, we don't need the scientists to show that song (pop, traditional or whatever) is profoundly important to human beings, and for reasons that elude simple cataloguing. But then--if you analyze it exclusively as a commodity, you lose the mystery of art.