If they are wearing on the outer edge then it's not sagging springs. That would wear the inner edge. To check the ball joints jack the tire up a couple inches then put a big pry bar under the tire and jack up and down while looking for ball joint movement.

I think someone aligned it wrong. I hate it when shops use alignment bushings on the top ball joint.
Also you need to follow the recommended tire pressure on your door sticker and the rotation schedule in your owners manual. That will help a lot. I think it calls for a cross rotation every 5000 miles. The fronts get crossed to the rear and rears come straight forward.