It's an interesting theory, but I don't think it holds up. Last I checked, most evolutionary biologists don't think it's that likely intelligence involved to get better at survival against the wild--as every other large predator species manages to get along without it--but a much more interesting hypothesis: we evolved intelligence to deal with/compete against each other for reproductive and other resources (see Dunbar.) It's apparently very interesting to see how different primates deceive each other--we're by far best at it.
Your explanation of stupidity doesn't really hold under that model. You have to pose something different--decreasing returns to general intelligence for the purpose of deception and social climbing, for instance. Since most of the socially dominant people I know are decently intelligent but not geniuses (and most of the geniuses I know are socially somewhat-capable but not politician level) this does make sense.
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