Micheal are you ascerting that even without the Americans' in Tunisia the Commonwealth troops would have defeated Rommel???.
I believe you are right about whole companies running and breaking up at the battle of Kasserine, but to my knowledge that NEVER happened again in Tunisia??? We of course did get overrun in the Ardennes much later in the war and for the same reasons in some respects as the debaucle at Kasserine. The facts are in combat that if the enemy has overwhelming mass he will succeed generally given fairly equal ground, this hasn't changed too much since Klauswitz wrote the rules of war (excepting of course the modern battle field which he could never have invisioned).
All of this is really moot, for the best way to model battles with CM IMO is to figure out what happened "generally" in various battles and try to match those capabilities using what the game offers to meet that goal, regardless of what "history" labeled the various troop qualities.