Nit: It seems backwards to measure efficiency in terms of kwh/mile. One would expect a higher efficiency value to be better.
No, that’s a sensible inefficiency measure. A sensible measure of X increases with X.
It also helps to compare costs, as 20mpg is far less efficient to 30pmg than 30mpg is to 40mpg, but the numbers suggest the difference is similar.
But I don't get why you think it's backwards! You want kwh/mile to be low. Basically, you want to use as little amount of energy stored in your battery to drive a mile. That's what that is.
For example: "Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg"?
There is good reason that the rest of the world uses the opposite system, and the reason isn't just that no one else uses gallons. It's that it's an objectively worse way of communicating fuel consumption in every single way that matters.
I'm surprised such questions come up often. Usually a current vehicle gets x MPG and a new one might get y. We use l/100 km in Canada. I think the primary advantage is it relatively easy to compute number of liters needed on a longer trip. It isn't super important however - better just to fill up!
PS I was mostly kidding about using MPJ. The numbers would be tiny and hard to make sense of.