I find myself often times wondering the same thing... but I'm a modern astrologer I suppose, so I find the "masclune and feminine" to be more qualitative rather than quanitative. Though I cannot say that isn't truefor traditional astrology either. But these ideas aboutt he "genders" of masculine and feminine applied ot planets began somewhere with traditional astrology and served a purpose. I just don't think at any point it was about masculine and feminine completing each other, and thus explaining the reason why we might desire what we lack. Synastry in astrology seems pretty dead-set on "like attracts (and is good for) like." I found this cool psychological study which epxlores that, it appears form the study, reality that like attracts like: http://www2.psych.ubc.ca/~heine/docs/similarity.pdf
I would say based on my experience with my boyfriend, both approaches would be correct.
I think the obvious reason that my boyfriend and I get along is that he has a 5 planet stellium including the sun in Sagittarius and I have a 3 planet stellium in Sagittarius including my Moon and Venus. Both Stelliums are conjunct. Then the opposite signs flush out the rest. Thus, as I always have said about him, he's exactly like me but not.