In a sense, he as the visual equivalent of Robert E. Howard. Like Howard, he is often copied, and well; unlike Howard, he is rarely surpassed at his own craft.
I'm curious as to what Magedalene's Egg means by this. Does s/he mean Frazetta was one of the greatest artists, while Howard wasn't one of the greatest writers? Or does s/he mean Frazetta was one of the greatest fantasy illustrators, while Howard wasn't one of the greatest fantasy writers?
I don't know why this phrase was necessary. It could've been left out, and little would suffer.