It's braking that destroys the kinetic energy that then has to be replaced by combusting fossil fuels. Without braking a hybrid car would be no better than a conventional car.
My previous car was a heavy Mercedes E320 cdi. I learned to look ahead and avoid braking and could get similar mpg to the current gti. It would return almost exactly 40mpg at a steady 100mph on the beautiful Spanish interior highways.
Unfortunately ordering the gti without brakes was not an option.
Also the gti is not the most aerodynamic car on the market (
https://en.wikipedia.org/wiki/Automobile_drag_coefficient ) so it helps to drive as slowly as possible in 7th gear.
But, hey, as somebody pointed out fun = 1 / (fuel economy)
https://photos.app.goo.gl/VXP4g1jr1xu6wSv39As you can see the average speed is 27mph because unfortunately I do a lot of town driving but even so 38mpg is, I think, quite respectable.
