The primals should have drop more philosophy and mythology, and ifrit battle should get an increase. It would add more options to the tome grinding. If you already have the weapon from each one of the primal for your main job (assuming ONE main job) - there is not much incentive to do it again. Unless you level arcanist which give you 2 jobs to choose from. Or go back and level ALL jobs I suppose - FATE grinding over and over and over again lol....