Never said it wasnt true just that there are variables to be considered.
All things equal, Wing Chun for the first 5 years Yes, beyond that the variables increase.
Teachers ability, students ability, fighting spirit, training methods, practical knowledge, physical ability etc, etc.
Both arts are also extremely similar, both employ neutralising principles against attacks, both have "sticking hands", both emphasise partner work for sensitivity training, both work off the waist, both punch linear, both deflect circular, neither has high kicks, both employ "uprooting" principles, both employ joint locks and chin-na, Wing Chun employs more elboy techniques, Taiji more grappling and throws.
Both are "soft arts" , both are "internal" arts that place emphasis on "fajin" energy.
IMHO - Here is a rather good rendition of a Taiji form performed fast. Notice the reduction in movements.
http://www.youtube.com/watch?v=jHitMFFbTZs
Compare those same reduced movements to these:
Pao Fa Lien Wing Chun
http://www.youtube.com/watch?v=w8ErY0gfLgY
Pan Nam Wing Chun
http://www.youtube.com/watch?v=mWT-e2N8m28&feature=relmfu
Variables.