What the author seems to ignore, or at least fail to realize, is that for any massive group, like the 330 million Americans, getting to The Top is intensively competitive. Even at the top 1% in cognitive ability, there are 3.3 million people to compete with. If all 3.3 million of the top 1% in cognitive ability were to go for Congressional seats, the odds of any random person from that group getting in are still about 1 in 7500. You need luck, skill, ambition, friends, money, proper habits, and infrastructure to be the top of 7500 similarly-skilled people. There's far more to it than "being smart" (and many measures of intelligence).
Really, the more amazing story is the large number of people in Congress who are in the bottom quartile... Sheila Jackson-Lee almost certainly has to be one of those. We can all name several others.
Also that using these selective, “elite” institutions as a criteria introduces another entire factor.
Even if the education you get at Stanford, Harvard or Yale is no better than at Podunk Jr. College, the people you meet and befriend at those institutions are going to *GREATLY* influence your odds of climbing the ladder; indeed that is the payoff for spending $50K a year - not the education, the connections.