If you was racing with sticky tires, then yes, your builder is right, but an everyday truck will not twist the axle that hard in any driving condition.
As a simple test, put the park brakes on and have a couple helpers push and pull the truck while you watch the pinion angle. If the springs are soft, it will rotate quite a bit.

Go back to equal angles and see how it acts.

1937 Chevrolet Inline-powered Streetrod