I would have to say that is a weak argument. Dogs would naturally run wild too, but we can train them to be house pets and they are bred, sort of, to be domesticated. Sure, horses are born to not trust people. But what is natural about NH is that we can learn to communicate to the horse, build trust, respect, and rapport with the horse, in a way that he would find easy to understand using horse psychology. Now, I do agree that some trainers out there say they use NH, but I disagree with the majority of them. They don't really understand what's going on inside the horse's mind, they just deal with the horse, and every horse, in the same or similar way.
Horses adapt very quickly to things. So they learn to adapt in our domestic environments. That doesn't mean that Mother Nature's instincts have gone away, but we can teach the horse to become calmer, smarter, braver, and more athletic, without doing it in a mechanical way that would be very unnatural. It's all about working with the horse's nature and understanding how his mind works. Knowing what's important to horses, what motivates them, was makes them afraid, what makes them resist the human.....all of that comes into play when learning how to be natural with a horse.