I agree, larger diameter is much better, but very difficult to live with in the car.
I limit my remarks to a single point of attachment, in which bending allows collapse of the adjacent tubes.
A properly designed chassis is a series of triangles.
To your other comments...I'm certain engineers who are very familiar with the chassis in question, and the forces involved in accidents, are involved in the establishment of these specs and rules. Chassis builders, OE factory engineers, safety experts, sophisticated CAD and analysis, etc. Fuel cars, Pro Stock, NASCAR, Big bucks. That all filters down to the lower classes.
Unfortunately, it usually takes someone being killed to cause a serious look at the cars in question and get them updated.
