The option isn't to disable parallax but to disable perspective zoom. With the latter disabled, the icons move the same amount but the wallpaper is not zoomed and moving in the opposite direction (which, when enabled, makes it looks like the icons move more than they do)
It's slightly jittery to me on my Air 2 and 5S. More importantly is I don't even notice it unless I look for it. I just realized I had turned it back on months ago after reading this thread.