> The "literalist" interpretation of Genesis is fairly recent

You mean Augustine and Thomas Aquinas didn't take Genesis as fact? How about John Calvin? Oliver Cromwell? Jonathan Edwards?

Bishop Ussher?

I don't believe that Genesis was seriously questioned before Galileo's discovery of craters on the moon (implying heavenly imperfection) and of moons circling Jupiter (proving there wasn't a single divine focus of motion and attention at the center of the earth). Before that, there was no reason to question it.

And, yes, Homer thought the Earth was a disk - with, perhaps, just enough surface curvature to allow ships' masts to disappear last over the horizon. But ancient ships weren't very tall.

What was developed much later was the idea that Columbus was the first to realize the Earth was round. (The post-Homeric Greeks beat him to it, though I'm not sure how well-known it was before mass education. After all, not everybody lived near the sea.)