Exactly.
I mean, it's not a universal thing, but if (taking the early crusade as an example) the Legiones Astartes is creaming off the Terran military academies' top hundred thousand male students in each generation....and killing or crippling ninety percent of them...then even if the recruitment rate is male-biased the way it is today, it's not hard to see why you're going to have a significantly gender-biased graduating "top class". Which, fast forward on a hundred years or so, means it's perfectly correct that so many senior navy officers should be female.