You keep saying that, but we've offered examples of why that's often not the case. Yes you will have one city that can build military units faster than any of his cities, but he will have two cities that can build military units as fast as your top two cities, with more flexibility on use of IW for other purposes and West Point. His army would overwhelm yours because you'd produce at an equal rate but manymore of his units would have extra promos, and he'd be able to use IW for other things while still using his NE city to always produce military units.
By the way, I'm a warmonger like you seem to be, but not everyone is, and seperating IW and HE is *much* better for someone who isn't always at war because IW can build those wonders you despise but which help with cultural victories while the NE city still builds units for defense.