I disagree with the explanation. I think its just a matter of the bell-curve. Many mediocre people, and relatively little high ranking, among both females and males. And the mediocre majority of females will tend to go for equal partners, hence mediocre men.
Mr Average hence is so popular because most women are Mrs Average and look for an equal partner.
That’s sort of close to what I thought, which was that women chose men who didn’t have the top jobs because those who did might be intimidating or they (the women) would constantly feel inferior to them… not so much a case of such men being “too good to be true”.