I believe that radio created Bluegrass, in a sense -- young country musicians, brought up in the Old Time styles of playing, were suddenly being introduced to Jazz/Swing via that new-fangled radio. Bill Monroe's mandolin swings in a manner we never heard in Old Time. That to me is the essence of what sets Bluegrass apart from its roots.

BTW, I can think of only two musicians who have created a distinct genre of music, at least in modern times. Bill Monroe, with Bluegrass, and Dick Dale, with Surf Music.