I'd concede that you have a point - up to a point, though. Once upon a time in my distant youth, in a different realm beyond the seas there was a special school with selective admission, which would probably be designated as "AA" in your setup. Children there were doing things like topology and 5-dimensional geometry while in tender 6th and 7th grades. That school was organized by university professors mostly for their own kids, but they had to open it to outsiders - and did so in the form of open competitive admission. I have VERY SERIOUS doubts that work ethics alone without at least "bright" IQ level would have sufficed there.
Not all children of bright parents are bright or motivated themselves. It takes both. In the system I remember, kids who weren't able to keep up with the "A" track had to move to the "B". Some of them couldn't keep up because they weren't bright enough, and others because they were lazy.