Well, also, "jazz" used to have a broader meaning than it now has. E.g., if Cab Calloway and Louis Jordan are jazz, then why aren't the Drifters and Chuck Berry? JB's antagonism towards the blues is well known, but that doesn't make it clear what her was antagonistic towards. About half of what Charlie Parker recorded used a 12-bar chord progression, and so does James Brown's "Papa's Got A Brand New Bag," but neither feels like blues, or like each other.

And of course a lot of JB's live vamps of, say, "Prisoner Of Love" or "I Lost Someone," were totally based on gospel. But maybe he thinks the "core" is something else?