"But even in his poorest state, Clapton didn't have the kind of experiences Leadbelly had."

You are reminding me of this article I just finished reading about hipsters and their over the top obsession with 'authenticity'. Most art in history, in fact the overwhelming majority of art in history, was made by artists that were NOT at the events in question, did NOT experience things first hand, are NOT from the culture being portrayed, etc. It's actually pretty rare for it to be 'authentic' in the way you seem to desire or even demand.

Imagine if "you had to be there" or "you have to be from this culture" was imposed on historical art, retroactively? There wouldn't BE art, in short order.