Board Thread:Speculation House/@comment-10380701-20141011082048/@comment-4010415-20151021214737

Basically, Yang's weaknesses are

1. Enemies she can't land a hit on.

2. Taking too many hits, thus losing too much Aura, which leaves her vulnerable to actual injuries and even death.

That's why she lost to Neo. She couldn't hit Neo, but Neo could sure as hell hit her and continued to do so, chipping away at her Aura until she was able to knock her out. And Neo would've finished the job if Raven hadn't shown up.