So you are saying all modern rock music from Elvis to Black Sabbath to Metallica should not exist as it is the “in” group taking the music of the “out” group, in this case the blues? People don’t work like that, culture doesn’t work like that. It’s constant borrowing, development, abandonment, rediscovery and remixing with very little regard as to what groups some people would consider “in” or “out” from their perspectives.