While there are significant differences in average physical characteristics between men and women, well, those are averages. The variances in difference between more and less fit men, and more and less fit women, are significantly larger than the differences between an average man and an average woman anyway. Since each character is uniquely fit anyway in M&B (as represented by various stats), averages are hardly relevant for player characters. And Calradia being as sexist as it is and war as male-dominated as it is, I think it can be assumed that the fighting women found there aren't a representative sample of Calradian women anyway, but a selection of the most badass, valkyriesque ones.