But why? Even if there's no tradeoff, what advantage would Albert Einstein have had over an average intelligence competitor for mates had he lived even a mere 200 years ago? Slim, I'd think. And who's to say he would have used that narrow advantage to win a mate of above average intelligence, vs. some other desirable characteristic?

Exceptional intelligence as a strong determinant of economic and social success (and thus presumably reproductive success) seems to be a relatively recent phenomenon in the human species.