It depends on how you set up the AOEs. Even on tactician enemies feel compelled to run through properly placed fire fields. I find it best to use harmful aoe combos as a way to soften up enemy groups or to cut off certain paths. Water + electric can be a nightmare for your melee if you use it while they are in the middle of a fight but if you use it on the enemies back line you maybe have perma stunned the enemy groups CC. Oil + fire can be messy if your melee has to run through it to hit targets but it can several weaken an enemy's front line if they are forced to run to it to get to your group.
Making the enemy come to you either by force or carefully placed traps can lead to nice payoff without endangering your melee.
For leadership I always put it on my main 2 characters since they can get a free leadership point from their traits. Have leadership on both means neither of them miss out on the bonuses.
