As quoted " After all, we are only talking about "opening a door", not bench-pressing 100 kilos." End quote.

"We are only talking about opening a door" is complete nonsense. You do not "open" the exit hatch, you physically remove it and then place it such that it does not impede egress through said emergency exit. If the pax in question cannot lift a 10kg bag into the overhead locker without assistance then that alone is sufficient grounds for them to be removed from the exit row. Secondly if said pax cannot hear and/or understand someone who is standing next to him when the cabin is relatively quiet (IE during boarding) what chance would they have of understanding, comprehending and acting descisively on crew instructions in the chaos, bedlam and volume of noise during a genuine emergency with a smoke filled cabin.