If I may, I feel there is some confusion of what a graphic novel is (or even what literature is) and isn't. A Graphic novel isn't a genre; it's a format, much like an audiobook. While it is often lumped and viewed distastefully alongside comic books, graphic novels come in as vast a range of genres as audiobooks do.
Visual/artistic Narratives as literature precedes the written language and limiting literature based solely on word count vs imagery would exclude a vast array of ancient and Classical pieces of literature, particularly hieroglyphics and illuminated manuscripts, such as the Book of Hours or the Book of Kells, which often contained substantial more artwork than written words, if any at all, and modern translations, such as The Prince, into graphic novel format.
As someone who has spent the past 9 nine years immersed in the academics of Ancient and Classical History and work in the wonderful world of books, after having read many of these posts, I get the sense that people are confused in what literature is. Literature, in itself, refers to any piece of writing that holds artistic merit, is both fiction and nonfiction and encompasess all genres, including comic books. We can't simply pass over a title because of a lack of understanding of what literature is. I've included a succinct list of academic sources at the bottom to help uncover the world of graphic novels!