Dimming to preserve night vision is far from ridiculous. Night vision repair takes a finite time and the brighter the previously light the longer night adaption takes
Best results are if the cabin lights prior to the event are of the same brilliance as the inner outer emergency lights
Clearly a matter of personal opinion. Both Cathay Pacific Airlines and Dragonair have a long held policy of cabin lights on bright for take off and landing at night; although of course set to dim in the cruise when passengers are sleeping.
Then of course you get the faintly ridiculous Qantas Domestic policy of dimming the cabin lights in broad daylight yet turning them to bright for engine start and once the engines are stopped on the tarmac. It was suggested dimming the lights during daytime saves fuel by using less generator load!
In fact it is mindless stupidity by whoever writes the policy manual used by the cabin staff.