As someone who has driven with regenerative brakes since 2005, one pedal driving offers only marginal improvements in efficiency.One pedal driving is always better than braking, but it doesn't mean you have to drive "choppy". Efficiency reduced by: driving faster (more wind resistance, more heat in the motor), accelerating quickly (more heat in the motor), braking (loss of energy due to friction), running accessories like heat. I am annoyed if I ever have to touch the brake when I am driving 1-pedal and I don't have an issue keeping my speed smooth (except when I am letting it rip!). Optimal efficiency case would be driving at a slow, constant speed. In an ICE, there is a trade-off in speed because you have different gears, but we don't have that issue in an EV.
If you can 2-pedal drive, but never touch the brake until you are < 5 mph, that would be something to see. Every time you touch the brake, you lose efficiency.
Where the Energy Goes: Electric CarsEVs are 60% to 73% efficient, depending upon drive cycle (77% to 100% efficient if the energy recaptured from regenerative braking is counted).www.fueleconomy.gov