In that light I'd like to mention supports.
Majority of supports are female and support dudes are mostly melee. There is practically no male support casters. There is Gragas (but he is not completely support) also Zliean (meh), I have seen Xerath (still not support), Victor? (noting much), Velkoz (I like that one), Galio (usable) and Fiedelsticks (not played anymore).
These are all but champs taken from other positions. On the other side there are female pure support casters: Nami, Lulu, Janna, Sona, Moragana, Karma, Soraka, Zyra. And I left out experimental ones like LIssandra, Oriana, Elise (used to be good), Lux, Annie.
This is how it is. And I am not complaining even though I'd love one or two male casters supports.
Woman and Man were always two symbols. Men - strong and rough. Woman - weak and gentle. And design is a lot about symbols.
Females should not be thought of as the "weak" gender
Physically they are. If you are thinking about mentality thats different story. Fact is that majority of men are stronger then women.
But in League there are strong women and they are great.
I am no women hater nor sexist.
At the end of the day you pick your champion not because he is he or she but because of his/hers skills and abilities.