European test are indeed stretched. The makers have had too long to figure out how to "cheat" on the tests. (Optimize for test conditions based on imaginary 70s traffic.) Hopefully the new testing cycle soon to be introduced will give better results.
As an example, a couple of years ago I drove my moms "super efficient" VW Polo 3 cylider Diesel on a 5000km around Europe. According to the manual that car can achieve 78mpg. The best the trip computer ever told me was 67mpg, while I was doing 50mph for 15 minutes on a perfectly flat road in Denmark. (I reset it for testing.) On rural roads in Norway I got 60mpg for 3 hours. Blasting an average of 88mph for half an hour in Germany (meaning I really was bouncing between 70 and 110mph due to traffic) it told me 33mpg. Trip average was 50mpg, but besides those 15 minutes in Denmark I wasn't really trying to drive economical at all.