Earlier quoted context omitted.
Ok, let me put it another way. If there is a variation for the amount of knowledge the brain can consume from human to human, assuming they're "healthy", it's gonna be something like Infinity x 99, infinity x 8, Infinity / 2. Whatever it is, it'll be a limit that's way beyond what a human being could ever reach in a lifetime.
So you don't believe that there's a spectrum of disability? You're either intellectually disabled to the point of not being able to dress yourself... or you're a potential Einstein - nothing in between?
This discussion is pretty difficult in that there are things we can't define. I don't even know if we're all talking about the same thing when we say "knowledge" and we can't define "healthy", and the term "capacity" for the human brain is assuming we all believe the human brain really does have a limit. I can only assume there is some kind of limit in the same way I assume if I traveled in a straight line forever I'd eventually reach the end of the universe. It's just imcomprehendably large and nothing we do in a lifetime, currently 100 years or so, will reach that limit.