Your first sentence doesn't even make sence. First of kung fu is a style, or you wan't to disagree with bruce lee. A system is based on effectivenes to take out the enemy. All techniques utilized within Muay Thai were designed to accomplish that. I can't say the same for Kung Fu. Jeet Kun Do on the other hand is a form. It doesn't stick to a system or style, it utilises the strong aspects of the fighter and builds a system if you will for that particular fighter. That is something totaly different.
When I would see a guy aproaching me and he starts doing a triple twirl wisslekick i'll step to the side and start hooking and kneeing him. Great moves for training your body, but suicidle in combat.
That's why kung fu fights resemble muay thai fights, because that stuf is to dangerous to pull of in real combat. Next to that I would like to say that muay thai is a lot easier to implement with grappling since the stance isn't sideways. Quicker sprawls and takedowns! Think about that.