They'll never do this. They would have to completely reworked the whole battle system. Yoshida and team think that the general player base can't comprehend "complicated" aspects like elemental affinity. Even defense is useless cause in most cases, survivability for certain fights are determined by the amount of HP you have. Example would be titan hm with 3600 HP. BLM would be completely useless in a lot of content with it's Super Mario flower fireballs. Speaking of which, is probably on of the most disappointing things in this game.