We think Tesla added more camber to the rear for a purpose. They need to design the car for everyone, not just for drivers with high-level skills. It makes sense for the car to come out of the box with alignment settings leaning toward understeer, as understeer is easier to correct compared to oversteer.
With thicker shims, lateral G will definitely be sacrificed. However, this does not mean the car will corner any worse since the front has limited traction from the beginning, as we mentioned earlier. From my personal experience with silver shims, the car still understeers into a corner if it's push it hard enough.