The human body is one of the most complex systems on the planet. To believe that a single input/behavior has that much control over the subsequent outcomes is just ludicrous, and all well-founded science supports that.
Does eating extremely well provide positive benefits? Duh, of course, but the definitive statements you are making are sadly just a feeling and not a reality.
While I am also using personal experience, what I can tell you is that because my oldest was diagnosed, we've gotten in touch with and exposed to many other families that deal with ADD/ADHD. I have not personally seen any evidence of what you describe, even for the parents/families that appear to fit your perspective.
Just because one got a 21 and one got a sixteen does not mean that the 21 is definitively better. In general, I think the scores themselves are meaningless, except perhaps as a general ranking mechanism.