You wanted to battle a Bison at his absolute best. So wouldn't it be fair to have Kahn at his absolute best too?
So with this in mind Bison is too powerful for anyone from Earth. But then Kahn is not of Earth. Kahn at his absolute best (as is Bison), has even killed and absorbed the power of the Elder Gods and conquers the universe. He becomes unstoppable. Which in his story ending, he goes mad as he has conquered everything and has no challenges left.
This alone would make Kahn the "absolute" master of the universe and beyond. Not even the X-Men, or any superhero alive can match that much power.
You have to go by the stories that are placed in front of you. And Bison don't even come close. Even if they didn't have powers, Kahn's strength, power and endurance, would overwhelm Bison.