The claim isn't that nobody is above their "level"; it's that black people are "likely" to be - and I read that as "most" are - above their "level".

At what "level" are people with good connections, powerful parents etc.? Is affirmative action more effective in advancing people than pulling strings and calling in favours? Isn't this mechanism - the social status quo - what affirmative action is designed to change?

Why would one expect more incompetence from one than the other?

It's well known, of course, that two wrongs make a right. It's also well known that all white people have rich, powerful parents. (Wasn't that a Dave Chappelle skit?)