To me, the keystone of the phrase "the great American novel" is not the word American but the word great.
Greatness, in the sense of outstanding or unique accomplishment, is a cryptogendered word. In ordinary usage and common understanding, "a great American" means a great American man, "a great writer" means a great male writer. To regender the word, it must modify a feminine noun ("a great American woman," "a great woman writer"). To degender it, it must be used in a locution such as "great Americans/writers, both men and women . . ." Greatness in the abstract, in general, is still thought of as the province of men.