I don't see it as a debate about "best" or even really "most innovative", just about individuals (or pairs in the case of Lennon/McCartney) that achieved a level of greatness (in terms of what contributions they've made to human knowledge/creativity) that logically you might expect to see a lot more of today given the vastly greater number of humans in existence now.
I wonder if "levels of greatness" is a relative quantity. If fourteen living composers are objectively as good as Beethoven/Lennon/McCartney (as one may expect with a much larger population), none of them will be recognized as great as Bach.
