You are indeed correct about the kicker that is airborne, but I have to disagree with you on the other point. Through the right positioning of the foot it is possible to create a stance similar to "leaning forwards" so that the force is not moving through the kickers body but is routed into the ground. I have seen myself a small old man pushing ("pushing hands") a huge bloke across a room without him moving an inch.

Point 4. with the kung fu kicks. It is not really true what you are saying. It is possible to kick or punch someone so that he flies across the room without you moving an inch. This is due to "rooting" of the body to the ground. That is, the force will be routed to the feet, which, if done right, will even strenghten the position the kicker is in.