As you know, Qian Kun Da Nuo Yi (QKDNY) is Ming Cult's legendary martial arts skill. It gives you special insight into enemy fighting, lets you redirect inner energy and other martial art skills, move your acupuncture points limitlessly around his body (the only other person who was able to this was Ou Yang Feng, and he was not able to do it as quickly and flawlessly like ZWJ), as well as other special tricks. The first person to fully master all seven levels was ZWJ, and with it, he was able to conquer all of Jiang Hu's martial artists.
Many people overlook QKDNY because ZWJ was not as flawless as Guo Jing or Xiao Feng or Yang Guo were with their own martial arts. However, this is only because ZWJ first of all hates fighting. Secondly, he is not an experienced fighter like Guo Jing, Xiao Feng, and Yang Guo are. Therefore, he cannot use his martial arts to his full potential. That said, ZWJ was still the best martial artist in his time period.
QKDNY in the hands of ZWJ doesnt show its true potential. Here's why:
Remember Yang Xiao? He was lucky enough to become Yang Ding Tian's (Ming Cult's Leader b4 ZWJ) favorite student. Therefore, he was lucky enough to learn 2 levels of QKDNY. He practiced that for at least 10 years. With it, he was already very powerful, being able to defeat Ying Tian Zheng as well as beat the group of Ming Cult specialists when they didnt want him as leader. Not only that, he was able to force Cheng Kung into a stalemate while still fighting the six Ming Cult high level specialists AND after taking two hard blows from Cheng Kun. Of course all this was done with many years of practice on only the QKDNY's second level. Note the words many years of practice.
As for ZWJ, he had all seven levels and was able to beat everyone in his time period. However, he did not have even a full day's practice of QKDNY. ZWJ learned QKDYN in a matter of several hours, and afterwards, rarely practiced the skill again.
What if ZWJ did practice his QKDNY. What if he practiced this martial art for several years, just like Yang Guo or Guo Jing practiced their martial arts for several years. ZWJ was just an inexperienced fighter, that's all.