Unchained is a *terrible* thing to use as a WAR: it eats your Wrath stacks while simultaneously preventing you from using Inner Beast. If you're using Unchained, you're reducing your mitigation.
Vengeance is a wonky ability because the damage it provides is dependent upon taking physical damage. As such, Stoneskin and Adloquium reduce its value. On top of that, it's on a really long CD.
Assuming 2.5 seconds between incoming attacks (doesn't happen in my experience; bosses tend to use magic/cast time attacks often enough that the incoming rate goes significantly), you'd be getting 6 ticks off of Vengeance every 48 GCDs. At 50 potency per tick, that's 6.25 additional baseline potency/GCD. On top of that, I'm not sure that Vengeance can crit, which could reduce the value of it further. The only time you'll really get a lot out of Vengeance is when you're AoE tanking with physical damage targets.
AoE damage and enmity are a more complex question than you might think. The PLD AoEs are effectively free: CoS has no cost and Flash costs MP. Overpower, on the other hand, is expensive as hell. If you use it more than 2-3 times, you're completely demolishing your TP, which means you're going to have empty GCDs when punching the boss later on. On top of that, Overpower deals laughable damage compared to DPS AoEs and has a much smaller area of effect.
This is further complicated by the vagaries of Flash's enmity generation. Supposedly, it doesn't scale with gear, is unaffected by Shield Oath, and all sorts of other factors that would render it effectively worthless. Getting answers to those questions would go a fair way towards putting some numbers down.
There are a *lot* more balancing factors associated with AoE enmity/damage than there are for single target damage/enmity. The reason I don't do the math for them is largely because it's a *lot* more math involved coupled with a *lot* of missing information.