We can all disagree with each other as long as we want, but as long as the rules say that anything with an on/off switch must be off while the engines are running on the ground, that’s just the way it is.
I know that it must be very frustrating to have to switch off all electronic equipment 20 minutes before landing on long haul flights and 10 minutes on short haul ones but we have to give the checks in good time and take our seats and there is no time later to recheck electronic equipment is switched off.