Many taijiquan classes lack 5 important elements necessary in order for taijiquan to function as a martial art:
Neigong (whole-body strength)
Martial concepts (what combat constitutes and how to do it effectively)
Chin na (the art of seizing)
Shuai jiao (take downs)
Jing (whole-body power)
Without these 5 components, taijiquan is lacking something and may not work in combat.