Dangermouse - I am afraid your comments regarding Nr control rather expose the difference between theoretical design parameters and the real world experience.
I am sure in one of your books somewhere it tell you that the engine governing system maintains the Nr inside strictly defined limits - that it does when power is applied but the droop law slope of any helicopter governor will have to shallow off at the bottom to prevent hunting in low power situations and, once the Nr is being driven up by other factors ie disc loading in manoeuvres, the throttle can only back off so far.
Low Nr isn't generally a problem in the Lynx since the engines are quite powerful and the governors work well - it is high Nr that can only be controlled by the pilot raising the lever that is the problem. A rapid, tactical descent followed by a flaring turn to wash off speed and make an expeditious arrival in an LS is the type of manoeuvre that regularly tries to wind the Nr off the clock in a heavy Lynx - adding to the AUM will just make it worse.
Your answer will probably be to train the pilots better! The condition is manageable at present AUM but will require even more pilot input and control (when he is trying to concentrate on not getting shot down) if you make the FLynx heavier. Helicopter designers are supposed to make each generation of military helicopters easier to fly so that the pilot can use the aircraft as a weapon of war to its best effect.
I would not for a moment exonerate the IPTs in the flawed procurement process but AW have been guilty in the past of presenting the IPT with a 'solution' to a problem in meeting the required capability which leaves the IPT with the choice to either accept the compromise or face further delays/costs in getting the product to the front-line.