It does not take a lot of input from the instructor or a lot of practice by the student for the student to learn to punch in natural motion. To gain any effectiveness from holding the hand in an unnatural position requires a lot of instructor input and student practice.
As I have stated before, my goal in teaching is that each student leaves a class better able to defend him or herself than before he or she entered the class. When a first day beginner leaves my class and is attacked in the parking lot, he or she will be better able to perform the natural horizontal punch that they were born with, and not be confused with trying to punch vertically.
Taekwondo also has it illogical teachings. A front stance is a natural stance that any beginner may perform easily, however, for pattern performance purposes, we teach that the rear leg should be straight and the rear foot should be parallel to the front foot. This is an unnatural position since it take a conscious effort to keep the rear leg straight and the rear foot twisted, and it puts undue strain on the Achilles tendon. However, the "powers that be" have determined that this is a more visually pleasing way perform the stance while performing a pattern. When performing patterns, a student is required to maintain constant, conscious thought to maintain this type of stance. The rear knee wants to bend naturally and the rear foot naturally wants to angle outward at about 30 degrees. I have been able to rationalize teaching this way of performing a front stance (straight leg and parallel foot) since the stance is only used this way while performing patterns, since the front stance is seldom used in fighting, because the stress it puts on the legs helps make them stronger, and because the concentration required to maintain the stance in this manner helps students concentrate, which helps them while learning other techniques. If the front stance were taught this way as a fighting stance, I would have a problem with teaching it and have to look for another school.