Well, the Passat weighs more like
3500 lbs. So, its not a far cry from 2x your Echo's weight. Second, cD is only part of the equation. cD times frontal area gives you the actual drag of the car. So, even if the Passat and Echo have the same cD, the Passat is physically larger so the frontal area is larger which means the overall drag is higher.
So, to answer your question, yes, the smaller engine would get better mileage in the Echo.