Its odd the everyone says that genetics doesn't play a very big role on rack size. yes, nutrition and age are very important.
Your problem is that you are applying too much common sense which completely escapes those that support ARs. No breeder of any animal would would kill off its best males and allow lesser animals to do the breeding. Even Dr. kroll admits that culling bucks before 3.5 yrs. is a bad idea, but in PA we cull our best buck at 1.5 and continue to cull the best buck in each succeeding age class.