Turn 4 basically requires, or implies you to believe:

-2 meele dps
-2 caster dps
-2 healer
-2 tank

I am pretty sure you could do it 2mnk/2blm or 2brd/2smn or 1drg/1smn/1mnk/1blm or whatever you want, as long as that is fulfilled. Therefor the Turn is pretty much tuned how its intended (you can't use 4 meele or 4 casters etc like you can on turns1-3)

Gear will make it a lot easier, also different kill orders can optimize the types and strengths of your players and job choice.