I remember when our teacher of "African American Musical Civilization" in college used to say "Davis didn't invent anything, he was an opportunist that improved

I remember when our teacher of "African American Musical Civilization" in college used to say "Davis didn't invent anything, he was an opportunist that improved what already existed". I don't have great memories of that teacher and, regardless of if what he said was true or not, doing what he said Miles did, is not a trivial and/or bad thing at all. In any case, I wish there were more "basic guides to X", being X whatever artist that has a certain level of fame and recognition which I fail to understand the reason for.