Earlier quoted context omitted.
I assure you that different people have different degrees of cognitive ability. What you say has some truth to it. But a deficit in preparation can be atoned for by a high degree of ability. And no amount of experience will carry someone who is simply over his head. That has been my experience anyways. We are not all geniuses though I wish we were.
Genius is primarily a learned skill. Yes, some people have more aptitude than others, but the vast majority, if they apply themselves, will do just fine. It's far more a question of a support structure to instill discipline than it is of innate skill. Those who truly cannot learn and maintain discipline are rare.
"Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated failures. Persistence and determination alone are omnipotent"