This is beside the fact that I think the nature of the elemental fist abilities is fundamentally flawed, you can choose to increase your damage by using the element the mob is weak to or you can use the fist ability that gives the most beneficial stat bonus to your situation, if either of these criteria conflict then the usefulness of the ability overall is shot in the foot from the beginning aside from any complications maintaining MP.
At the very least they need to rework the impact the elemental effect has on the nature of your damage, as it is using an element the target is resistant to kills your damage completely. If the Fists abilities are to be useful outside of niche situations where 1) melees are viable and 2) the mob has a particular elemental weakness, they need to tone back the elemental aspect and emphasize the associated stat bonus. If your damage per fist is 100 on, say, an Earth Elemental and you use FoE it shouldn't plummet to 15, MNK is a physical DD and their damage should be predominantly physical. Having only 3 elemental fist abilities is retarded if you're going to make the chosen element such a huge factor in damage dealt because it leads to you either owning the shit out of a mob (something weak to fire) or doing mediocre-to-crap damage because there is no elemental weakness to exploit and the target resists elements you actually have (something wind based, can't use FoF or FoW, and if the mob isn't weak to Earth you might as well not use FoE either).
The decision of which ability to use should be first and foremost in the stat boost if offers with the element aspect offering a very minor boost or penalty based on the target's resistances. I should be able to use FoF when I need pure damage, FoE when I'm soloing, and FoW when I need mobility or find myself with a surplus of ATK/TP, and I should be able to do so without having these options completely taken away because of an arbitrary elemental resist.