> I think the point is that bipedal could be more energy efficient than wheels and that feet can go where wheels can not.
The second one, absolutely. As for the former, I don't think you can get any more efficient than a wheel on a flat track - certainly biped movement is a lot less efficient since you need to work against gravity.
The perceived efficiency of bipedal movement comes mostly from the ludicrous efficiency of biological actors when converting chemical into kinetic energy – a cyclist (or even runner) can go a day on the chemical energy that would get a motorcycle to the next petrol station [0].
Also consider that even the fastest bipedal runners tend to go much slower than any motorised vehicle, and even quadruped animals rarely reach into what is considered standard with cars.
[0] The guideline daily amounts for a human are roughly 10 MJ, from personal experience, cycling a bit during the day only increases that marginally (e.g. 10-20%). It seems reasonable to claim 1 MJ per 100 km cycled, whereas one kg of gasoline (~1L) is at ~42 MJ. Given the usual 1-10L/100 km, 1 MJ appear to correspond to a few kilometres.
Here is a trivial proof of the former: take an elite biped marathon runner on foot vs an older marginally in shape biped like myself on a bicycle, and on my bicycle I can beat the elite runner quite easily.
Another way to model it is I can quite easily maintain 10 MPH without much if any sweating on a bike trail, but on a calm hike with the kids on the same trail I struggle to achieve 3 MPH average.
The second one, absolutely. As for the former, I don't think you can get any more efficient than a wheel on a flat track - certainly biped movement is a lot less efficient since you need to work against gravity.