If the momentum of the front and rear drivetrains are equal while coasting (in both setups), then how can it be seen that off power coasting is affected? I agree with you that the velocity if the car, and the wheels are spinning at the same rate, but energy in the rear drivetrain is greater due to the freewheeling.
It can be seen in the last picture posted (granted that no wheel slip is happening when coasting) but the energy present in the rear wheels when power is off, remains.