Overpower

[TouchandFeel]

Given that Overpower is a directional AoE (unlike PLD and DRK's), it seems like it would be difficult to use reliably when you're running around trying to pick up adds.

While Overpower may be a little harder to initially get a hang of, it is really not all that hard to use after a little bit of practice.

Overpower also has it's advantages compared to Unleash and Flash. For starters it does way more damage than either of the others. It also has a greater reach (8y vs. 5y) which allows you to tag the group from the edge of them instead of having to be right in the middle of them. This is really useful when doing a mass pull because you can tag groups as you run past while staying off to the side instead of running straight through the middle of them which can help keep some distance between you and the trailing mob pack and therefore lessen the amount of auto attacks you take during the pull. It also provides greater range on the mob pack when you are tanking them since you try to keep all the mobs grouped on one side of you between you and the rest of your group, so if it is a really big group that is not tightly packed you are more likely to hit all of them.

Also Unleash has better ease of use. Abyssal requires a target, while Unleash just requires said targets to be in range.

While Abyssal requires a target, it also can be cast at range which is incredibly useful and valuable since you can tag groups from a distance such as when you run past in a mass pull without getting too close or if a group spawns during a fight and you want to tag them all without moving.

So which one is more "user friendly" is debatable since one requires no target but requires you to be in the middle of the enemies which may require you having to move to them, while the other requires a target but allows you the flexibility of hitting them from range.

...abyssal drain wont reach all adds, since its a smaller circle ...

Abyssal Drain is not smaller than Unleash, they both have an area of effect of 5y.

The only instance in which Abyssal may not hit all targets while Unleash would is if the mobs spawn in directly surrounding the player. In such an instance, the target requirement would offset the area of effect of Abyssal to the side the target is on and potentially miss some mobs on the opposite side from the target.
In my experience this can pretty easily be compensated for by proper repositioning and targeting.

Okay, I've seen this before, but since the game doesn't explicit numerize Enmity gain for various skills, does Unleash generate less Threat than Abyssal Drain?

Unleash generates a lot more aggro than Abyssal, but shouldn't be used for dps purposes in any circumstance. Only use Unleash to grab groups of adds, or increase your aggro meter when you really need to in trash pulls. Abyssal should be used as a dps gain in mobs of 4+.

From what I have seen, Unleash does just under twice the agro per use compared to Abyssal Drain for a smidge less MP, while Abyssal Drain does a bit over twice the damage of Unleased for a smidge more MP.
https://www.reddit.com/r/ffxiv/wiki/enmity

Basically Unleash is way more MP to agro efficient while Abyssal Drain is way more MP to damage efficient.

As maintaining agro is widely considered fairly easy and damage is seen as more valuable, Abyssal Drain is seen as the superior of the two abilities.

In most cases Abyssal will be your "go to" AoE agro ability, however in instances where a high level of snap AoE agro is needed Unleash may serve better depending on other factors such as where and how the mobs spawn.