I'm not disagreeing with you, I'm agreeing with you
I'm just saying kitkat in general gives older hardware more tangible and perceivable performance boost than it does on newer hardware. This is regardless of Art v Dalvik, but then the additional benefit of Art where apps are pre-compiled means it should give a benefit to that older hardware by making apps load quicker and less stress on CPU at launch.
The second point I was making is that despite googles efforts to make kitkat more beneficial to older hardware, very few older machines/devices will ever see 4.4 which is a shame.
Indeed just looking at my own google developer account stats, it seems majority of apps I have developed are running on much older android hardware (android 2.2.3) than 4.2, 4.3 & 4.4 combined ...