In the Bakhtin post below, I borrowed from Bakhtin's ideas to suggest one of the signs of genius in an artist is the ability to penetrate the souls of others. To examine and understand and show the psyche of one outside the self.
I would suggest another sign of genius in the artist--the ability to interlock themes so closely that to discuss them separately is pointless.
In David Henry Hwang's M. Butterfly, Hwang explores the stereotype of submissiveness. When I teach this play, I write that on the board in capital letters: Stereotype of Submissiveness. It could be a simple theme, I suppose. In Hwang's skillful hands, though, it is extremely complicated. You cannot separate issues of sex, gender, race, culture, and nation from a discussion of this stereotype. Hwang develops the relationships between these topics tightly. You cannot in any meaningful way discuss one without the other. Hwang also uses his considerable skill to examine how art, culture, and fantasy contribute to this stereotype of submissiveness, and then shows the devestating effects.
You can't peel a theme away from others in M. Butterfly; Hwang too closely connects them.
I see similar interlocking in Morrison's The Bluest Eye (though a certain level of cause-effect relationships between these themes makes them less interlocking and more, I don't know, cause-effect related).
Perhaps this interlocking is what can make a political or social work of art truly great. To make insightful connections, and present them in a personalized, humanized way (nobody does this better than David Mura in Where the Body Meets Memory: an Odyssey of Race, Sexuality, and Identity, where Mura makes an incredible connection between his own sexual addiction and the Japanese internment camps).