Very true, for beginners that have no fighting expereince, they must start with constant punching to get the muscles properly align and develop force and energy control. Augment this, with push ups.
Punching in ngo cho kun is done with the arm staying close to the body and during the release the forearm twist with the fist acting like an arrow head goes for the target.
Just like any blunt instrument the principle to penetrate a wall is to have a twisting effect an arrow, a bullet or a drill bit is a good example and this is what ngo cho kun punching technique is about.
The first two big knuckles must line up with the wrist and with a jerking motion the fist twist into the target. The legs, the hips and the shoulder must provide the main push for the fist to penetrate the target not the arm, and then tensing at the last minute the strike, to give it a solid impact the twisting will give it a penetrating blow.
After months of training, the best way to test ones self is to spar in full contact. For safety reason, wear body armour, groin guard and maybe shin guard. Spar with open fist. And try to land a power penetrating punch at each other no head blows only body attack.
A well place punch with penetrating power would penetrate the body armour and would either fracture or cuase bruises on your opponent. A punch like that would knock the win out of your oppoenent making him unable to continue the fight, then would you know that your punch has that speed and penetrating power.
The body armour can be like the ones that tae kwan do uses or armour reinforce with bamboo sticks like kendo armour.