Problematic stance exposes your weakness in the eyes of an expert (ninja).
A lethal problem with today's kung fu horse stance (马步) is the locking of a practitioner's waist because on impact, the external force cannot channel down to earth. As shown in the above picture at left, not only the person's impacting force is jammed at his/her waist, the knees are locked too. So a skilful opponent can use techniques to break the left person's waist and knee at once.
In that sense, it is not good for a person who practices horse stance in long run as it not only hurts his/her waist but also his/her knees. I have seen many martial art exponents have shaking hands and lags during old age.
A better solution for our body and for combat is using higher stance that can channel any impact forces down to the earth as shown above. In this sense, a ninja has a much better solution as he understands the actual harming of opponent only takes place within a distance of one inch. So before a kung fu fighter realises what had happened, his waist, knees and feet are already injured.
I am not interested in martial arts, but I have treated many people with waist problems. Perhaps it is time for us to reflect if rigorous martial arts trainings are indeed appropriate. Bear in mind that in old days, people seldom live more than 70 years and our life is much longer...