Well, if everyone had the capacity to shift form (even between male and female) at will, sexual dimorphism exists. On a person who does X arbitrary exercise units, the male form will be proportionally stronger for the same regimen I am told. So a bias would definitely form; the only question is whether it's a society of men who can girlshift, women who can boyshift, or if it depends on culture.
I'm still going to vote for my society of lesbian werewolves, though, and no amount of logic or reason is going to stop me. u.u