Bikes are more efficient than walking, but that's only because roads are flat so wheels make sense, right?
Does it make sense to say that this fact is simply gained by putting a lot of energy into making the earth flat, into making tarmac and putting it there?
What you are saying does make sense, and ties in with some of the points made in What makes running so much less energy-efficient than bicycling? Although you mention "putting a lot of energy into making the Earth flat", I do not think you are making an economic argument. You are merely asking if the superior efficiency of cycling is due to the fact that we have flat roads to cycle on.
Yes, cycling on roads is more efficient than walking on them because tarmac roads and bicycles (or cars) have been designed to work well together to make an efficient system of transport. Efficiency is only one criterion : cost, comfort and flexibility are some others.
Energy is lost in cycling mainly because of rolling resistance, due to the deformation of the tire. If roads and wheels were made of hard steel, and roads were perfectly smooth and flat, the efficiency of cycling would be even higher because the deformation would be far less - though much less comfortable if there is even the slightest bump.
Going up hills, the bicycle loses some of its advantage because you have to do extra work to raise the bike (7-20kg) against gravity, as well as yourself (around 70kg).
Cycling over rough ground (using a bike designed for roads) can be less efficient than walking over the same ground. In the extreme, cycling through a boulder-field is almost impossible, even on a mountain bike, whereas with practice and good balance it is relatively easy to step from one boulder to the next.
