Yea seriously it is a bit ridiculous considering i have to get to 3 stacks of grease before i can even start to reach max dps, which means 3 full rotations. You will barely reach this when pulling trash mobs in dungeons except maybe on the 3 mob if it is a group of three, mean while bard, drg, smn, and blm just unleash their full potential from the start just about (exception is drg since they do have a few positional requirements for debuffs/ buffs)

Then when we talk about bosses a lot of them have moves that take them completely off the battle field or a mass aoe you need to run from. Ifrits charges and garudas shriek for example. By the time those are done with, grease is gone and you need to re build all the stacks over again.