How does Tommy's character relate to the southern ideal?

Tommy Johnson is a talented black blues guitarist, who claims to have sold his soul to the devil in exchange for guitar skills. He plays "Man of Constant Sorrow" with the Soggy Bottom Boys, but leaves when they get into trouble. He is eventually discovered by the Soggy Bottom Boys at a Ku Klux Klan rally, about to be lynched.

As Matthew W. Hughes writes in his article, “Cinethetic Racism: White Redemption and Black Stereotypes in “Magical Negro” Films,” “In O Brother, Where Art Thou (2000), the only two black men in the film are both MN (magical Negro) characters: The first is “Tommy Johnson” (Chris Thomas King), a young, out-of-work hitchhiker whose magical prowess with a guitar is due to a pact with the devil, and the second is the “Blind Seer” (Lee Weaver), who is a blind and tattered railroad push-car operator who offers spiritual and sage advice.” The “Magical Negro”—a term popularized by filmmaker Spike Lee—is a stock black character in American film that comes to the aid of the central white characters and is endowed with mystical capacities. While the trope is not explicitly anti-black, it devalues black subjectivity and character in favor of white projection and a kind of marginalizing idealization, which has its basis in racist logic.