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 ...