In fact, the goal of Diversion is to limit enmity generation when you have a big Burst, like BLM. I've a good BLM in my FC, and he uses Diversion for his burst. And when, during the fight, is enmity is too high, he uses Lucid Dream. The fact is for the SAM and the MNK it misses something.
@wereotter -> With tanks, we agree with the fact that cross role skills idea is mostly bad. Take Tanks for exemple: the game let you choose between some skills, but in this list you have: Rampart, Provoke, Shirk, Reprisal. These 4 are almost must-have in raid, even Shirk - that let your MT playing in DPS mode.
For dps is quite the same, we have: Second Wind, Invigorate, Goad, True North (at least for MNK, DRG and SAM, it's really important to have it), and what? And "dodge-bump-mechanic", Diversion that works only for some jobs...
By that I want to say a lot of "cross role skill" are too much important to not take them, we really have 1 or 2 skills to choose, and they're not really usefull for most of them. The spell to dodge bump for example, were do you use it? In Shinryu ex? It's always usefull, since Tidal is easily "dodgeable".
So the "optionnals" skills are often "obligatories" skills...