You are of course right, provided that the girls chose Zack, and not sex with his penis. But if we consider the option of sex, then the ways of God are inscrutable, the winner of the dragon becomes the dragon himself. And then Zack becomes vulnerable, there are many girls, and he cannot split into several Zacks, so why not throw him an option when the girls start cheating on him due to their increased sexuality. Zack is not a god and is as vulnerable as everyone else, simply because there is no absolute weapon. At least this would reconcile some with the fate of Felix, preserving Zack's achievements.