Q29: Do you have any plans to implement elemental weaknesses/resistances? Also, please tell us why you eliminated these.

A29: There was already a lengthy response about this on the Beta forum, but to give you an example, if you are fighting Ifrit and his weakness is water, then classes and jobs that are proficient in fire would be excluded from participating. Since we want to make participating in content easy with the Duty Finder, we felt that this wasn't good and decided to get rid of it.

Is that not evidence enough that they chose the easiest way to design their game?