I tend to disagree that dimming the cabin lights makes no sense. For the experiment, I recommend that you try to leave only the emergency lighting on next time you have a couple of spare minutes on the ground at night. It's not even close to the normal cabin lights in terms of illumination. And the procedures assume the worst-case scenario, in which normal lighting becomes unavailable on the ground for whatever reason. The slide lights are not a culprit either as they are not directed into the eyes of descending passengers. Their purpose is to illuminate the area right in front of the slide so that people have some idea of what they will be stepping onto once they jump off the slide and start running away from the troubled aircraft.