I forgot how much burn damage BFB does but depending on your odds of critting, the extra crit rate might be more valuable. Then again with Eye for Weakness you could use Grease and set up for other companions as well. But then AGAIN you have to consider whether using a turn to set up Grease is worth it.
Yeah this sort of questioning can go on for a while, especially when it hits the point where you have to consider just how much time you're willing to spend on a battle. For some people they're perfectly fine taking turns to have the most secure strategy, while others are fine introducing risk for the sake of moving things along quicker. That's not really a right or wrong debate so there's no definitive answer there.
I'll say this though, if you're considering Perfect Positioning, your crit is decent, and you're using elemental attacks, you might want to consider Black Mage with Arcane Penetration to have that -25% resistance for free. Not sure what that maths out to in damage but it might be more certain than banking on crit if it's too low.