I think what needs to be remembered by those of us who were there when Check Berry hit the radio waves, was the cultural impact he had, rather than whether he was the greatest guitarist, the first to play that general style, etc. Sure, he, like ALL musicians, borrowed from what came before and went off in at least somewhat his own style.
However, for those of us old enough, remember the impact hearing him on the radio had. It was big and influential. Looking back at it from the distance of time, it would be arguable what greatness he may or may not have had. But remember when we first heard him, what was typically on white American radio at the time, and we remember him in that cultural context. Being able to do so is the way to put him in proper perspective.
Whether individually we were fans of his music and style or not, we can't deny his impact on the radio listening audience as a whole. He was very (not solely) instrumental in paving the way for what was to come in rock and roll of that time.
Tony