That is a common misconception. Cars with bigger CC usually have more torque and can be geared lower hence having lower shift points and cruising rpm. I was on holiday in australia in March this year, and we rented a 2010 Ford falcon with a 4000cc inline 6.
at 110 kmh speed limit, the rpm was 1800. I was impressed with the fuel economy of that car, and this experience forever changed my perception of large cc cars.
What you said is true. But larger CC cars also idle using more fuel than a smaller CC one. So during a traffic jam they wouldn’t fare as well.