John Byrne gave us a very alien, sterile Krypton, with inhabitants that were implied to be hairless going by lack of eyelashes/brows, and the reaction of Supes' mom upon seeing an earthling. (please log in to view the image)
Did the Kents opening his matrix chamber somehow alter Superman's DNA? He obviously looked more human. Bulkier, with body/facial hair. (please log in to view the image)
Krypton's been revamped many times since then, but was that version of Supes mutated to a small degree?
He's clearly much stronger then your average Kryptonian, looking at the New Krypton series. And DC policy has stated for years that Daxamite > Kryptonian. Superman being = to most Daxamites shows he's a particularly powerful example of his species.