But this is about poetry, would Twain qualify as a poet?
My vote would go to Edgar Lee Masters because the spoon river anthology is one of the few poetry books I actually read, and it exemplifies a lot of the American spirit, IMVHO.
The vast majority of Cervantes's work was not in poetry, either. I think the idea is more "emblematic national storyteller" than poet in the narrow sense.
It's at least arguably about storytelling. You don't sit around the fire talking in verse for your entertainment.
For instance, one of Homer's works is in the news due to a film being made of it.
I suppose that suggests the Coen brothers.