Because the lever (arm) on one side is longer working against the fulcrum (chassis), affects the suspension (load) at a different rate. In other words the long arm twists the bar easier, no?
That does happen. Are you still trying to suggest that if we mismatch holes side to side that one side will be stiffer than the other? It won't because the rotation of the torsion bar is not pinned to the chassis. The forces will balance out through the torsion bar.