Let's compare the process of 2 hair removal feats:
1) Duan Zhengming was behind Elder Kurong. Kurong didn't bother to look or turn behind. He simply put one hand on Duan Zhengming's head, spoke a few words, and when he lifted his hand, there was not one hair left on Duan Zhengming's head. Had a special hair-removal knife been used instead, it would not have yielded such flawless results as Elder Kurong demonstrated.
2) The wind emitted by Murong Fu's sword was unbearably shivery to Duan Yanqing, Cui Baichuan, etc, so much so that their hair were being snipped off by the sword wind. In addition, their clothes were being ripped into pieces by the sword wind.
One should note that while Elder Kurong simply moved his hand and the deed was done, Murong Fu needed to go nearly all-out to get it done.