the young guy was crazy.
the cherokee will be better on fuel... hell, with the v6 it will still be better on fuel!
as mentioned, the cherokee has a zero parasitic loss type 4x4... when you are in 2wd, you are only running 2 wheels.. NOTHING extra. until slippage of course(unless you switch the mode button to snow or something else). the pat and compass system is older and has loss in 2wd mode (things spinning, etc.). also, there is no switch in those cars to "turn off" 4x4... only to engage 4x4... meaning in the 2 wheel drive mode, it still acts like an awd drive vehicle.
hope that helps.