Perhaps what we need is science, which means that methods of defence must be validated empirically. I think that many real-world experiments have been carried out, in the ring and in the street. Moreover, these techniques are seldom used by their advocates without substantial modification. This creates inefficiencies in the learning process. I will demonstrate this with several lines of argument.
Young babies have a rudimentary ability to ward-off unwanted contact.
Try to wash an unwilling infant's face and you will see blocking and ducking both. We have characteristic blow avoidance responses that may be innate. The natural blocking response for a threat to the head from a blow or a falling object is to place the arms over the head and to cower, the approved airplane crash survival posture. Essentially what people do is to put the hands in the way of a threat. When you learn formal stylized blocking motions, you are generally told that your cocking motion will be followed by a bone-breaking block.