I'm surprised that this subject doesn't come up more often.
The nameless Shaolin Janitor Monk (AKA the "Sweeper Monk") from DEMIGODS & SEMIDEVILS is generally acknowledged as, by far, the greatest fighter in the entire Jin Yong canon. He was truly a fighter without rival, but could the DGSD trio of brothers, Kiu Fung, Hui Juk, and Deun Yu, have beaten him . . . or at least given him a reasonably good fight?
The most direct measure of the Janitor Monk's superiority was the ease with which he dispensed Siu Yeun San and Mo Yung Bok, two fighters generally regarded as being in the same category as Kiu Fung. The Janitor Monk defeated them both quite casually, but there are a few considerations here.
1. Neither Siu Yeun San nor Mo Yung Bok were prepared for the Janitor Monk's intervention. They had never even imagined such a fighter existed, so naturally, their guard against his intervention was nonexistent. At the time the Janitor Monk intevened, Siu Yeun San and Mo Yung Bok's attention and energy were focused exclusively on each other.
2. Siu Yeun San and Mo Yung Bok had been fighting for quite some time before the Janitor Monk intervened. They were likely both exhausted, and neither is likely to have put up his best resistance against the Janitor Monk (not that they could have beaten him, but perhaps their showing against him would have been less pathetic if they had both been 100% when they faced him).
3. Siu Yeun San and Mo Yung Bok were old men, past their prime (the Janitor Monk was even older, but he was far superior to them in martial arts regardless). Younger men of equal skill and ability (i.e. Kiu Fung) might have fared better.
Siu Yeun San and Mo Yung Bok, in terms of raw power and skill, could be thought of as equivalent to two Kiu Fungs. However, neither fighter, though generally in Kiu Fung's class in terms of skill and inner power, had quite the same ferocity and unique fighter's instinct that was Kiu Fung's alone (not even Siu Yeun San, Kiu Fung's biological father, had this instinct to the extent his son did). Moreover, even the combined inner power of Siu Yeun San and Mo Yung Bok would not equal that of Hui Juk, who had the combined inner power of the Siu Yiu Sect's three most powerful elders. Hui Juk's inner power was likely second only to the Janitor Monk's (although it's difficult to measure how great the gap between them was). On top of Kiu Fung's prowess and Hui Juk's hellacious inner power, there is Deun Yu's 6 Mak Divine Swords....considered by some to be the most dangerous martial art of all. Deun Yu also had the Bak Ming Sun Gung skill of inner power absorption. In light of all these factors, could the team of Kiu Fung, Hui Juk, and Deun Yu, knowing what to expect and fully prepared for a showdown against the Janitor Monk, actually have a chance of beating him? If not, could they at least give him a reasonably good fight?