In my example, Uchi Mata, there is enough power/kinetic energy transfer to lift the other guy off his feet, rotate him over his head and then land him on the ground. You have the power of your entire body using its strength plus the power of his body under the effects of gravity and the additional acceleration that your strength applies to him. Uchi Mata (or any throw really) is using the energy from both people, where a kick is only using the energy of one person. If I weigh 200 lbs and throw a kick... at most, I have 200 lbs being accelerated, providing momentum and inertia. If I throw a 200 lbs opponent... then there are 400 lbs being accelerated, providing momentum and inertia. I am not great at physics... but last time I checked accelerating 400 lbs into motion took a lot more power/kinetic energy than 200 lbs.