The female characters are weak because of their desperations attacks. After all, desperation attacks are the only things in this game that make the characters different. Squall's, Zell's, and Irvine's desperation attacks all hit multiple times, making it very easy for them to do massive damage. The same can't be said for Selphie's or Quistis's attacks, and Rinoa's multiple-hit attack is rare and unpredictable.

There's also the fact that, of the three female characters, two are completely undeveloped beyond "naughty teacher" and "I like trains!", and the third one is a useless whore.