It's not so much that the technique itself is especially sneaky and tricky; it's more a matter of Yeung Gor's opponents having NO IDEA that he has this in his back pocket. It would be equally unexpected if he abruptly pulled a move from Hong Lung 18 Palms: the opponents just wouldn't see it coming.
So if Yang Guo has one move that can disable Linghu Chong in one blow, superior agility, superior trickery, and decent all round martial arts, what would Linghu Chong have in a fight? Yang Guo can out-dodge him, and put up a decent fight in any scenario, is better at tricking his way out of a situation, and if things get close (and it's not like LHC is any good at hand to hand anyway), YG can knock him back with one blow. What does LHC going for him?
I think a few of you are overstating the role of Ha Mo Gung in Yeung Gor's repertoire. West Poison Au Yeung Fung only taught him very little: it was basically a one-night crash course. Ha Mo Gung's role in Yeung Gor's martial arts development is analogous to the role that Mongolian wrestling played in Gwok Jing's martial arts development: it was the first thing he learned. Gwok Jing was able to draw upon his skill at Mongolian wrestling to catch Au Yeung Fung and other powerful opponents off guard once or twice, but that skill wouldn't carry him to victory. Likewise, Yeung Gor used Ha Mo Gung against very weak opponents: the Mo Brothers when they were kids and had hardly begun training in the martial arts and crappy 4th Generation Cheun Jen Sect newbies. Even that hit on Lee Mok Sau was a lucky strike because she was arrogant and didn't see it coming, and it didn't really do her any serious damage. Superior agility is debatable, but this is very early Yeung Gor, before he had even learned the Jade Maiden Manual's skills. I'll give him trickery (though Ling Wu Chung was no slouch in the wily moves department).
Ling Wu Chung at this stage of his life/career has operated in wulin for a few years already. He already has some notoriety as the head disciple of the Mt. Hua Sect, and is able to hold his own for a short time against the likes of Teen Bak Gwong.
At the very least, this is going to be a good duel. I don't see it as being one-sided at all.
Yeeep totally agree YG might be have better martial arts and skillset but LHC more "adapt" and "proficient" with his own skills proven by HYS comment that if YG want to beat LMC he need at least 1 years to fully mastered HYS Divine Finger and Jade Flute Sword and 3 years to clearly bettered LMC..