What I like about resistance training that you don’t really get out of punching and kicking is that you can easily measure your energy exertion effort to determine whether or not you are truly pushing yourself to your maximum limitation for that specific moment. Meaning, I can tell you to punch, but you can punch with minimal effort and then you will not be receiving much physical benefit from that exercise.
But if I tell you to go under a bench and press up a certain amount of weight, you are forced to exert yourself in order to accomplish that assigned task. I can tell you to run, but if you rather decide to walk than run, then you will not be receiving the physical benefits of running. Therefore punching and kicking alone does not involve enough of a physical challenge in order to transform your body to an optimum level of fitness.
You have to punch and kick the right way, with maximum exertion in order to receive the physical benefits of that body movement. If I tell you to run a mile untimed, you can decide to walk, and then you will not be challenging your body enough to take your fitness to the next level. But if I tell you that you have to run a mile within 5 min. that will be another story, now you will push yourself to your limits to achieve that goal.
When I tell a person to punch or kick, he can punch or kick like he is walking or he can punch and kick like he is sprinting. If he punches and kicks like he is sprinting, he will be exhausted, but his progress will be hard to gauge. It is not like calisthenics, weight training, or timed cardio training, your progress in kicking and punching is not easily measured.