I would be inclined to think the noticed difference in grip, is actually a result of the changed 4 link arm lengths and the way they make the vehicles body supply load to the wheels. And the changed pinion angle is just an unwanted result of adjusting the arms.
I believe you could correct the pinion angle by cutting the link arm mounts off the diff and rewelding them with the pinion set on the correct angle. And still have good grip with good pinion angle.