@alcpone
well i drive daily my xli with stock tyres of general and i do apply some hard braking ,,,but there is no swaying at all,,,,,some skidding is there but thats normal ,,as with any car..........my car swayed on M2......not because of brake application but i think due to a freak gust of wind............
i think ur friend should check the diggy,,,if there is some unbalnaced load there,,the car will sway.........and to me the older version of gli/xli...with round back lights had greater skidding and swaying problem than the new version with flat back lights of LED......i dont know ur friend has which model.......but if its old one,,then i think he got to live with it,,,,somehow ,,with some minor adjustments..........
i apply the brakes ,,as i did with cultus,,very hard and right in the middle of road,,but as of now,,no problem has been faced by me.