Kiu Fung himself once thought that he would not be able to defeat Deun Yu's 6 Mak Divine Swords. Indeed, it's true that Deun Yu's inner power was higher than Kiu Fung's, and 6 Mak Divine Swords was the one martial art that even Kiu Fung feared. Moreover, Deun Yu's Bak Ming Sun Gung and Ling Bor Mei Bo would make him like no other opponent Kiu Fung had ever faced.
That being said, Deun Yu was never really a fighter, whereas Kiu Fung was one of the most talented (if indeed not THE most talented) fighters of all time. If Kiu Fung really, really had to...say to save a life or even an entire COUNTRY, could he find a way to defeat Deun Yu?