It is but if you abuse it within limits of the roads, you won’t see any worse than 270/280 to a tank... can’t be foot to the floor all the time on the roads.
Drive it gently expect 320-350 on average.
For what it is, it’s incredible on fuel.
Here are two MPG figures calculated throughout my time in my S3 and my RS3, when I had my S3 I had a gentle commute which was around 4000 miles of its mileage so I’d expect it to be better.
S3 310PS; 11,800 miles... 25.11MPG
RS3 400PS; 19,400 miles... 24.98MPG.
Think that says all you need to know from the MPG calculations and when I drive the RS I tend to drive it.