I haven't seen it yet but I doubt there's a mention of African-American country music performers such as DeFord Bailey playing the Panama Express who was the first performer on Judge Hays' Grand Ol'Opry. Was it mentioned that Merle Travis learned from black man Mose Rager or that Bill Monroe from Uncle Pen and Elvis from
Big Boy Croodup? Then there's Charley Pride and the Georgia Yellow Hammers.
And the revival group North Carolina Chocolate Drops with Rhianon Gidens.

I think it can be shown that the Southern accent is a derivative of African-American
speech.