I get what you are saying. But our ancestors also had to jump on top of prey, and drive spears into huge animals. This requires great force. The body evolved in a manner that can generate this force.
Er actually it didn't. Human body structure has little to do with hunting, more to do with locomotion (in our case walking) and having hands free to gather food and use tools. Our bodies in structure resemble closely those of the other great apes who do not hunt with spears and jump on prey. At least that's what I was taught a few years ago during my MSc.
If someone were to hold out their arm and it were totally immovable I wouldn't call that natural, I'd say it was decidedly un-natural and quite an impressive skill. Yet most people can't do this. Let's assume that gifted athletes can, they have to train hard to be so good at what they do, it isn't like they're born being able to run 100m in 10sec. They have to train for it. Your use of the word natural and all it implies would have us think that cavemen could do all these things and that we have lost the ability over thousands of years as we have become more modern. Perhaps it was lost when Adam had a fruit salad he wasn't supposed to? Perhaps this is a reflection of what happens as we move from childhood to adulthood? We lose our natural ability to move naturally and fall down and cut our knee and run to our mothers crying?
Sorry I just don't believe it. I understand where you're coming from but I think the logic and language you're using is thwarting your argument. This movement isn't intuitive in my experience, it's a skill that has to be learned like any other. You position that it is natural movement possessed by athletes isn't totally wrong. If you watch films of Parkour for example the exhibit a good amount of mind and body coordination, same as other sports. Trouble is that amount of coordination is just the beginning step in my experience, there is a great deal more to learn.