I'm not sure this is correct. I might endorse a statement to the effect that fluid g is necessary in order to learn the more advanced skills of distinguishing sophistry, but very few people, high-g or otherwise, actually learn such a skill.

"Seems reasonable" is not a valid criterion for judgment.

Your claim is factually incorrect. The ability to tell the difference between sophistry and valid arguments rests on two things: first, awareness of the standards of validity, and second, the capacity to override the convictions that come from our associative thinking and evaluate the situation rationally.

High IQ permits people to come up with very complex and sophisticated rationalizations. It doesn't help them distinguish rationalization from rationality.