"""Genetically, looks and brains shouldn't be linked at all and I do believe there is no serious (anti-)correlation here."""

How did that "should not" come about?

How about creatures with worse looks (less attractive to their species), cope up by being smarter to turn sexual selection in their favor?

The notion of "looks" has not just come about in the last century or so, it exists even in totally foreign species, like flowers (attractiveness to bees by features/colors/smell/etc).

And looks have been shown to correlate strongly to sexual selection (from big tits to body fat).