who says that?
Doomsday was created on Krypton before Kryton was even an inhabitable planet. He was a science experiment that was sent out into the extremely hazardous atmosphere of Kryton and left to survive. During his generations on the planet Doomsday was killed hundreds of times over only to be brought back to life with a resistance to whatever previously killed him. I believe he was constructed out of DNA aquired from some really powerful people at the time.
Superman was thousands of years away from being born when Doomsday was created. Krypton became inhabitable while Doomsday was off ruining the galaxy.
And Doomsday would kick the shit out of Hulk before Hulk got the chance to get angry enough to over power him.