It is not automatically inefficient. In Zurich, I have around 5 supermarkets near by, walkable in about 5-10 minutes. Don't even need a bike. Taking the car would increase my travel time, not decrease it.

So my walkable city is more time efficient and has health benefits for using your own body instead of a machine to do the traveling. It's better if we measure for time efficiency and health. And it shows. Looking around, 95% of the people here, at least those not in cars, are healthy, slim and fit. All as it should be. What else would you optimize for?