I came close to saying something like that the other evening. Things seem to have become much worse in the last 5 or 6 years, and it's possible to find discussions that shortfalls used to be 5% years ago, then gradually 20%, and the worst examples now are over 30% down, touching 40%
In a way this is still understated and things are even worse. If a car claims 60 mpg and achieves 37.5 mpg, this is described as only 62.5% of what it should be, 37.5% down. But actually it means the car will spend 60% more on fuel than the driver hoped (think about how much to go 300 miles, 8 gallons versus 5 gallons). The continental system of figures, fuel per distance, rather than our reciprocal distance by fuel, is actually a bit more sensible. Even the country's moneysavingexpert would wrongly say 60 mpg is 20% better than 50 mpg. No, the cost ratio shows it's 16.66%
I occasionally look on a site called spritmonitor, German but with English language available, where people enter their own real world figures. I hadn't checked before, but it turns out to have electric cars as well. A car which claims 93 miles range has about 60 or 65 miles on average.