Because Superman isn't just a little stronger or faster than Thor. He could roll through the entire Avengers roster as though they were made of tissue paper. His speed is sufficient to go to the other side of the planet in a few moments, his durability great enough to tank planetary terraforming that shot from one side of the planet to the other end. His strength is enough to outright kill other beings of his nature, and he of course had to overpower that beam.