They built them to crumple tail gates and make operating the gate impossible in certain situations? Well, like I said, whatever blows your dress up. ;-)Fords got more articulation in those tests. The solid axle/coil spring trucks were/are superb off road along w some frame twist. I'm pretty sure they built them to flex but still be strong.
There are arguments, well made, on both sides.Articulation is good, frame flex is bad.