As a non rabid feminist (I hope) I would say that men are more suited for frontline duty has nothing to do with their brains, if you are referring to intellect but because of evolution which has made the human male physically stronger and more aggressive. Males and females across all sexually reproducing species display gender-specific behavior in many areas, including mating, territorial marking, aggression and parental care.
The higher level of testosterone in the brain of the male is critical to developing and activating brain circuits that control male territorial behavior and aggression. This has been necessary to ensure that the male could protect the female and children to ensure survival of the species. Which is why men are even today far more likely to commit violent crimes than women.
Evolution has also given men better spatial and mathematical skills, rank-related aggression, and other characteristics. This may account, scientists say, for the fact that there are many more male mathematicians, airplane pilots, bush guides, mechanical engineers, architects and race car drivers than female ones.
In comparison evolution has developed the human female so they tend to be higher than males in empathy, verbal skills, social skills, a more acute sense of smell and security-seeking, among other things,
While I will agree that these differences make men better suited for frontline duties I fail to see how these differences can make men better adapted as leaders or any of the other careers you refer to, that more men go into these areas does not mean that they are better at the jobs any more than saying a female nurse or a woman in any of the other traditional women's jobs can do the job better than a man could.