You summed it up perfectly.
A faster car qualifys top and we put them at the front. If their car deteriates in balance with full fuel, all will to different variying levels but never enough to make a massive battle of cars on our hands.
Imagine....
Watching Alonso, Hamilton,Schumacher, Button, Massa come through the field whilst battling each other. You'd see button nip past barrichelo with alonso trying a cheeky one too, potentially being 3 cars abreast down the straights where barrichello had held up button so alonso was close on his rear wing as they came on to the main straight.