Okay, I can't quite just let this go unanswered. Yes, Robert Johnson seems to have listened to lots of blues records carefully, and learned their lessons well. When I listen to Kokomo Arnold, Lonnie Johnson, and especially Leroy Carr, I hear lots of stuff Robert Johnson got from them. Yes, RJ learned a lot from records. But it's just as clear to me that a lot of his music reflected what was in the air in Mississippi at the time. The Library of Congress recordings made by Son House, Muddy Waters and others a few years after Johnson's death touch on some of the same musical territory.
And in the end, Robert Johnson's achievements surpass his influences. I have no interest in arguing about whether Johnson was the "greatest" or "most important" bluesman of all time, or of his time, or whatever. To me he, was like Bach - he represents the highest peak of a musical style that was already becoming unfashionable; at the same time, his music pointed toward the future and the next steps in the music's evolution.
Saying that Robert Johnson learned blues from records is like saying Bach learned music by copying Vivaldi - in both cases, it's kinda true, but ultimately not really important. His music, like J.S.B.'s, far transcended its influences.
Yeah, I agree completely - Robert Johnson was a sponge, a thief, or whatever you want to call it. BUT - he turned whatever he took into something his own. That's some of what artistry is about.
Whether Robert Johnson was "the best" is strictly a matter of opinion. As far as I'm concerned, someone who says any musician is "the best" is pretty foolish.