Dook Goo Kau Bai's martial arts: powerful, but one-dimensional?
The life of a wulin warrior is kill or be killed. Very simple. Either you are a better fighter than your opponent and vanquish him/her, or he/she is superior and vanquishes you.
And on this metric, Dook Goo Kau Bai and his esoteric sword techniques get the job done.
We know from following the adventures of our favorite wuxia heroes, however, that winning fights, while of paramount importance to life in wulin, is not the only dimension of that life that matters.
Dook Goo Kau Bai's sword techniques are good at vanquishing opponents, but they do nothing else.
If you have suffered grave internal injuries that threaten your life, health, or ability to continue functioning in wulin, various internal training manuals such as the Bak Ming Divine Arts, the Yik Gun Gung, the 9 Yum Jen Ging, or the 9 Yeung Jen Ging can help you heal, but the Dook Goo sword techniques would do nothing for you.
If you need to elude an enemy that is pursuing you, various arts increase your running speed, levitation ability, or ability to go stealth and become difficult or impossible to detect. Dook Goo sword arts do not accomplish these objectives for you.
Overcoming hypnotism? Need to hold one's breath for an extended time? Gaining resistance or immunity to poison? Various arts can provide these functions for you, but Dook Goo sword techniques will not.
Dook Goo sword techniques are great for winning fights, and while winning fights is a big part of wulin life, it doesn't encompass all the needs of a wulin warrior. If Dook Goo sword techniques have a downside, it's that they aren't versatile.