When Cheung Mo Gei defeated Ah 3, the external form that he used was Tai Chi Fist Technique. Granted, he was backed by 9 Yeung Jen Ging inner power and Keen Kwun Dai Loi Yee, but if he had used a hard technique to defeat Ah 3, it would not have been nearly as graceful. Inner power matters, and if yours is insufficient compared the opponent's, you're in for an upward battle, but if the inner power is comparable, then a soft technique such as Tai Chi increases survivability against aggressive, hard techniques.