So you need some account of where the car design comes from. [...] you'll find humans, with common human genes that construct common human brain architectures.

Yes, but what does this do to constrain your expectations about economics? If your intelligence idea is applicable to economics, it must have some explantory power that standard economic approaches lack (failing that, it should at least reformulate standard economic insights in a simpler setting).

A general theory of intelligence designed for constructing AI's does not need to be universally applicable. It's not a weakness if economics isn't one of its applications (after all, economics manages to get very correct results by assuming a simplified homo econimus that does not exist, so correctly moddelling economics is not a good test of the underlying assumptions), so there's no need to insist that it is.