First, let's concede when wheels are better. Unaided (but versatile) human-power transportation involves walking, climbing, swimming, or running. As many hikers of the Grand Canyon may have learned the hard way, going downhill can be more taxing than hiking uphill. Going downhill requires constant effort to stay one's descent as the maximum controllable walking speed is less than 3 mph and running downhill on twisting paths with thousand foot drop offs can be terminal. So walking man is not very adept at walking downhill. Doing so takes a lot of energy to avoid falling down.
Cycles have no difficulty going down moderate slopes. None whatsoever. Doing so is effortless. Gravity provides all the energy required to overcome rolling resistance and aerodynamic drag. The only issue comes when steep slopes lead to high terminal coasting speeds that, without functional brakes, can prove fatal. Cycles, like humans, must expend considerable energy to stay their headlong descent into out-of-controllness. The energy, however, comes at no cost to the human. All the energy is dissipated by the friction brakes as heat and small particles of brake pad, or a direct-drive hub motor could go into generator mode and use potential energy to recharge the battery. Either way, the human gets a free ride (or gets wasted if the brakes fail).
So on moderate slopes, wheels are infinitely more efficient than walking as no human-power at all is needed. Human-power, however, is insanely better at going uphill. Going up involves energy, but humans can climb vertical cliffs and even the marginally fit can climb vastly steeper slopes than any cycle (not designed to only climb steep slopes) could possibly get up. No cycle can climb a 45% slope with a bit of loose material on it, but humans can not only climb such a slope by lapsing into their slow and steady hoofing mode, but they can push the bike or pull the trike up the hill too. On a slope that the most powerful e-bike would merely spin its wheels, an ordinary human can climb by putting one foot in front of the other and make it look easy by comparison.
Pushing a bike up a very steep slope involves a push, hold the brakes, step up, then repeat. A trike can be pulled using a strap. Each step froward involves a surge forward, but adding an elastic section to the tow strap dampens out the surging motion. A trike is easier to pull up steep slopes than a bicycle is to push, and arms are free to help climb. Pulling a trike uphill for hours can be trying, but it is doable, and doable is vastly preferable to impossible.