That's assuming it makes the least bit sense to compare the distances people typically walk when that's the available mode of travel compared to how far they ride when they have e-bikes. And "sustainable" isn't even primarily about energy efficiency - it's about ensuring we don't exceed the capacity of the planet to repair what damage we do it. A human population that relies primarily on walking (or push-biking) to get around is almost certainly going to be far more sustainable than one primarily using e-bikes.