Dark Knight and Incoming Live Letter 4.2 on 12/15/17

[Claire_Pendragon]

You normally don't fight multiple enemies that hit for the same amount of damage as a single target.

In the example, I was more so referencing a situation where they do, so in this case, you killed 2 or 3 enemies in a group, of all the same type of enemy, and you have 1 remaining enemy, who was the same type.
(only by the example, and yes I wasnt being very clear with where I was taking the example. As a side note, the amount of dmg a target hits you for, doesnt effect the amount in which it heals anyways, so its not a factor for deciding if its worth using really. It's just to paint a picture.)

Your comparison ignores the damage though and only describes the HP gained. The only reason Drk sustain is 'viable' on packs is because its an AOE move that adds up to a ton of potency. Youd never use DAAD on a ST just because of the crap damage. You also seem to only be referencing the DA cost of DAAD in the view of a % of damage received. But on packs of stuff, they all hit like pansies so it will be much more 'sustaining' as a measure of keeping yourself up than a boss that AAs for 20k a hit while you DAAP 1 target for 1000hp.

Drk's single target sustain is non-existent while its AOE sustain on fluff damage packs of dungeon mobs 40 ilvls below you is pretty respectable. Theres no real mixing of those 2 categories for drk now.

The fact Abyssal Drain is better on multiple targets (for damage) isnt the argument, but the healing's "cost" is the argument. (obviously it heals more, on more targets, but its cost doesnt get cheaper per target, only what the cost offers, but its offer is offest by the amount of extra number of targets attacking u now, aka they cancel out)
The healing does have 2 requirements.
(1) Abyssal Drain be cast
and
(2) Dark Arts be active.

For arguments sake, lets pretend Abyssal drain isnt a requirement. (You are right, that its an additional cost)

If you could just hit Dark Arts, and then another button to eat the DA, just to land a heal, equal to what you would get from DA/AD, it wouldnt be worth it.
It's an emergency last option.
If youre out of CDs to lower damage, or you're down a healer, then it's worth the MP cost.

The argument is half "The number of targets" and half "is it worth using the MP?"

The number of targets is irrelevant to the MP cost, but as you mentioned, is relevant to abyssal drain, as its a requirement.

Now, the alternative is to use Soul Eater in case you dont have a healer.

If there is 1 target, Soul eater is the better for self sustain.
If there are multiple targets, Abyssal Drain is better than soul eater in self sustain.
But even if its better than soul eater, that doesnt make its MP cost worth it.

So I brought up the example of using on a single target, to explain WHY its not worth it. (But there are exceptions where it is.)

I think this should help explain where I'm coming from with this better.