Thats true in overall displacement, but when it comes down to displacement per cylinder, the dodge takes the cake, especially with the new 6.7l motor. 7.3 has .9125 liters per cylinder, 6.0 has .75 liters per cylinder, 6.4 has .8 liters per cylinder. 5.9 has .983333 per cylinder, and now the new 6.7 has 1.1166666 liters per cylinder.
But theres a whole lot more to power in a diesel, then just the displacement.