How should we walk barefoot. The bottoms of our feet are sensitive to impact and will teach us to run gently, if we pay attention. Shoes provide more leverage against the ankle, thus increasing the risk. I've never suffered sprained ankles, knees or anything while barefoot. With footwear, I have experienced sprains several times.
Sensitivity varies with the terrain.
Feet become desensitised on rough surfaces, but sensitivity returns quickly on soft surfaces. Living heels are not like a bicycle seat, which wear out with use. Exercise stimulates growth, and thickens the cushioning. Secondly, if you are running hard and fast, you shouldn't be landing on your heels. Heels are more for resting, than hard running.