You sure don't know what you're talking about.
In MT, the supporting leg is twisted with the BALL OF THE FOOT, so if ever your supporting foot is flat on the ground, you're doing a huge mistake.
MT is a scientific martial art, which means, it does not contain any type of technique that will harm yourself through over use, except if you keep getting punished by the opponent. This implies that no matter how many times you kick, you will not get hurt unless you're doing it wrong.
The reason why you twist your body at the ball of the feet is that your sole will have less fraction with the ground, as you almost completely lift up your ankle and heel, and it will also result in the foot and knee being parallel which is not detrimental to your health.
The MT kick is a powerful one, and very unsafe if you don't know what you're doing. Experience will be your teacher.