basic kata by design are too stiff, IMO.
in terms of punching, Goju is perhaps closer to boxing with less or no lift in the heel - but the weight is still on the balls of the feet. the only difference to natural stance is turn the front foot in a bit and bend the legs slightly.
watch these clips: all core rotation..http://www.youtube.com/watch?v=8pW_cDgrFaw
lol...don't give me a hard time for pointing to that-just to contrast with hip torquing/whipping.