Dunno what the issue is here but both have suffered from the same actions of the Horde:
Had their cities devasted by the Horde.
Had their people murdered by the Horde.
Had lost loved ones by the Horde.
Had their land taken and or destroyed by the Horde.
Sought vengeance against the Horde
Heavily dislikes the Horde
Jaina is the "villain".
Genn is the "hero".
I don't understand..? Is it because of their gender or personality?