> Google “smartest people in the world” and most of the results will be physicists, mathematicians, computer scientists, and chess masters.

Clearly not chess masters.

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> poorly defined problems [are also] everyday questions like [...] “how do you figure out what to do today.”

I think that I do have a sensible answer to this question, but the problem rather is that my answer is very different from what I am obliged by society to do. I can easily believe that a less intelligent person would not immediately see this discrepancy, and thus be happier.

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Concerning

> Christopher Langan, a guy who can score eye-popping numbers on IQ tests, believes that 9/11 was an inside job

and

> they’re still unable to solve basic but poorly defined problems like “maintain a basic grip on reality”

Being intelligent does not mean that that you have the same "trust anchor of truth" as many other people in society have, even if you assume that they are perfectly rationally thinking people (and I personally believe that being very smart and being a rationalist are only loosely correlated (you must be somewhat smart to be a rationalist, but the other direction (smart people are very rationalist) in my experience does not hold)).