The problem with a), is that often women aren't allowed to compete on merit, or they have to perform twice as hard, twice as often as a male colleague in order to prove it "wasn't some fluke."

Also, who decides on "merit" and "ability?" Most real-world problems are not math equations with clear answers. In that case, a homogeneous group is going to decide that merit is based on their group's definition. A diverse group will create a broader definition that accounts for a wider array of ideas and approaches.