From what my understanding on Wing Chun, it's designed based on direct defense and attack from start, i.e. self-defense skill, similar to Karate. While the rest of the traditional Chinese Martial Art (including Tai Qi), is designed based on body strengthening and skill all round plus postures. The defense and attack skill comes along the way with a stronger body and skill. So they are of totally different in nature.
I only learned wing chun and cannot comment on the others. Fully agree wing chun is a no-frills combat art. Didn't quite understand what it means by "skill all round plus postures". In wing chun, you need to make sure your stance is right and the arms are placed correctly too (as for effective defense and attack). True that wing chun is not brute force but the sifu told us its the power from the joint (don't ask me what this means, I am just repeating what he told me).
My previous remarks was mainly on 'practise slow, use fast'. My sifu's explanation was that if you cannot do it right slowly, trying to practise fast is just hiding the errors (hard to spot).