It would appear that the Ford F-150, the most popular car in America, has an average MPG of 23 mpg [0], so there's possibly some accuracy here. I do understand that's a very American-centric view, but its one explanation.

[0]: https://www.caranddriver.com/ford/f-150

American driver here, I don't know about others but my small hatchback gets between 30 and 35 mpg. If I am driving on the highway, I can get up to 37 ~ 40 mpg depending on what speeds I use and how hilly it is. NE Georgia.

Smaller cars and diesels are more common in Europe, which probably helps statistically. But I imagine the method of testing mpg between Europe and the EPA in the US could be different and is likely contributing to some of the discrepancy. Also didn't VW get caught lying about their numbers?

I thought VW lied about emissions not miles to the gallon, and the numbers I've said are what my dashboard shows for avg consumption when I'm driving, they ain't the testing numbers (which do tend to be ridiculously high)

24mpg seems right. I drive a pretty medium sized car - Subaru Outback - and I pulled 25.5mpg on a big road trip. My right foot is a little heavy.

Trucks and the fat SUVs that are super popular here get astronomically bad fuel mileage. Think low 10s MPG. Even worse when towing stuff.

Small cars do alright but are decreasing in popularity. Looking around the parking lots I frequent, where everyone has new vehicles, it's insane. All SUVs. Even when it's dominated by "smaller" SUVs like Mazda CX-5, Honda CR-V, Toyota RAV4, Lexus RX370... Those are still big boys.

One thing that I am hoping to get introduced to is better sources for the data points I use. I think they are mostly ok but I am no expert, so I could easily be citing something that is generally understood to be incorrect. Also, I could be citing very biased sources without even knowing it.

In particularly, this number of 24mpg (as an American) seems pretty in line with my expectations, so I decided to use it.