Why myth? I really don't get your dismissive response to the idea that, yes, there are great artists, and yes, they do create from themselves, and no, they don't do audience polling ahead of time.
It's something not just confined to...ahem...'Art'. In general you can engage people more if you tell a story biographically. The Second World War in Britain engages far more if you put Winston Churchill as the hero figure; the Civil Rights Movement generally gets hung round the personality of Martin Luther King; and, of course, WWII in Europe was all about the ambitions of Adolf Hitler. It's not hard to see why the tale is told that way; but if you really want to analyse those events then something much more complex emerges.
Similarly, the tale of Bebop is easier to tell hung round a few juicy personalities (Parker or Powell or whoever); the origins of jazz...Louis Armstrong, Sidney Bechet, Bix Beiderbecke etc of course.
That's not to deny the enormous influence individual musicians can have on shunting things one way or another. But the 'myth' of the great artist (or the great man in history) is just a winning way of telling the tale, not what really happened.