EV mileage doesn't account for use of climate control, lighting, and battery temperature management, hydraulic/electric pumps for steering, brakes. (Climate control for the batteries) you already know that it takes lots of electricity to run electric AC and electric heat, in your house. So these will cost a lot of MPG in pure electric vehicles. High speed driving lacked braking regeneration energy and requires now energy per kilowatt than aloe speed driving. You might get 4mpge/kilowatt at 50mph, but half or less of that at 80mph. Mountainous driving will also affect it.
I don't think anyone knows for sure. What we do know is that the Bolt EV motor is significantly more efficient than the Volt motor (at the least, the Gen 1 Volt) because it includes an additional stator winding ring. Look up Weber State videos by Professor Kelly. He does a good tear down and explanation if that's what you're looking for.
EPA testing allows the manufacturer to turn off all external power consumption, including Daytime Running Lights. So while the test cycle is realistic for about two thirds of the population, the creature features aren't used. The raw number becomes the CAFE value for the vehicle. Then the EPA uses a conversion factor to "account" for the creature features and this value ends up on the Mulrony sticker.
Switched reluctance motors (SRM) have been around for a while, but I think Tesla is the first to scale them up to that much power. While they have similar to efficiency to typical PMAC motors (like those used in the Bolt EV and Volt), SRM tend to have a bit better power to weight ratio and are capable of higher rpm.Model 3s rear motor seems to be a real design breakthrough.