I agree with you for the most part but the rule is so obtuse and tough to write because the sport is played at such speed. It tries to acknowledge that a runner who is trying to be evasive might inadvertently cause a defender who was going to be in a legal position suddenly be in a legal position.He dropped his head and hit with the crown of his head.
If there are going to be pass plays and tackling, there are going to be hits like that. I don't like it and I'm super down on this sport because I think the players have just gotten too big and too fast. There's too much force in this sport for the human body to handle.