Your last paragraph — interesting theory. Could easily see it being true.
There are exceptions, of course. Rare but spectacular. I'm thinking here of Meryl Streep in The Deer Hunter. Ms. Streep is not in the same league, beauty-wise, as Jill St. John, but her character (Linda) is heart-rending and unforgettable. I don't know where Ms. Streep ranks in terms of IQ points, but I think she's no dummy.
I know she's a big lefty, but so was Steve Jobs.