I think that most "end of an era" musicians are derivative. It seems inevitable as all that material is there, whereas it wasn't there for the "pioneers". J.S. Bach is highly derivative and he made no bones about it. In my opinion RJ added to the pieces he played. He didn't just copy them. The difference between "Love in Vain" and "When the Sun Goes Down" is a telling example.

Having said that, I find that when I am thinking, "what shall I play," I very rarely Choose Johnson. I think one reason is he is too "busy". His pieces are full of geegaws which are not related to each other.

I agree it is futile to try to pin-point the "father of the blues"; but do keep in mind that Blind Lemon Jefferson had made records already when Charlie Patton and Son House were developing his style. House tells Alan Lomax that he learned the blues from somebody who learned from Jefferson records.

Murray