The change itself, also, is pretty minor considering how few jobs actually use both TP and MP. Paladin, Bard, Dark Knight, and Red Mage if I'm not mistaken are the only jobs who use both. For every other job one of the two resources is pointless. Like no melee DPS needs MP, no healer needs TP so as they change the battle system, it makes sense to only have one resource as opposed to two since it just means adjusting a few jobs to make them run on one resource.