Both good points. The expander ball does have a job to do. As it is pulled back put of the case neck, I pushes any dings outward and rounds the neck mouth if it is oval or egg shaped for some reason. But if the neck is in good shape and round, you can use a bushing die to size the neck on the down stroke without an expander ball to iron it out on the up stroke. I have started doing this and it does improve runout.
Another option that helps is to remove the decaping pin and use a seperate decaping die for that. Then use the expander ball, but loosen it on the decaping rod about one turn. This allows the ball to free float more and helps with the runout. It is not as perfect a no ball at all though, since the neck dragging on one side of the ball more than the other contributes to the run out also. Lubing the inside of the neck seems to help there, but then I have lube inside the neck. Yuck!