The one area where Dark Knight actually doesn't have a case to be made for already being balanced in terms of "healing" is that it lacks a direct, non-rotational heal that isn't a part of its standard mitigation suite. Warrior has Equilibrium, Gunbreaker has Aurora, Paladin has Clemency, and Dark Knight doesn't really have anything. If you squint really hard you can kind of see where they meant for Abyssal Drain to fill that role, but it obviously failed at that job even before they merged it with CnS in your singletarget rotation, because AD is a rotational ability in AoE which constricts its use as a directed heal, and even when it was used in singletarget, the 200p you got from using it on one enemy was basically nothing.
I think it would be a reasonable ask for Abyssal Drain to be A) Completely decoupled from Carve and Spit, B) Removed from your standard AoE rotation, and C) Rebalanced to be a reasonable, usable self-heal in both singletarget and AoE, with an MP cost that makes it a modest DPS loss on use.
Something like:
A) Decoupled from Carve and Spit: No longer shares a cooldown, AD no longer restores MP on use.
B) Removed from your standard AoE rotation: Because you currently get 150 potency of AoE damage from AD, that potency should be added to Flood of Shadow to maintain your 'ideal' AoE DPS. Buff Flood from 160 to 190 potency (Sanity check: In AoE you generate about 15000 MP per minute, which is five uses of Flood, so a buff of 30 potency per Flood maintains the current level of maximum AoE damage, without making Flood a DPS gain over Edge on 2 targets.)
C) Remove AD from your standard rotation: Give it a 3000 MP cost, and make it deal 350 potency of damage to the first target, and 100 to any additional targets, healing you for 600 potency on the first target, and 100 potency for any additional targets. Change the cooldown from 60 seconds to 30s, 25s, or 20s.
- In singletarget AD would give you the option of replacing an Edge with AD for a 110 potency loss in exchange for a 600 potency heal.
- In two-target situations, AD would probably become your preferred MP spender, dealing 450 total potency to Edge's 460, but returning a 700 potency heal.
- In three-target situations, AD would fill the same role in relation to Flood, dealing 550 total potency to Flood's 570, but returning an 800 potency heal.
- In larger AoE situations, AD would generally be a DPS loss compared to Flood at 100 potency to Flood's 190 (except for the initial target, obviously), but would become a relatively powerful heal.
- For fewer than six targets, AD would heal more than it currently does (600+100n compared to 200n for n<=5), at exactly six targets the heal would be identical (600+100(6) vs 200(6)), and at larger pack sizes it would heal less (1300 to the current 1400, for 7 targets, for example). However, it would be held until you wanted to use it, to make the best use of it, and you could potentially use it more often than you can now.
- In singletarget, the self-healing would be somewhere between 1 and 1.5 casts of Aurora in total healing, depending on the cooldown, split up between 2-3 instances of 600p healing, with a 20-30s cooldown between them. This feels fair, considering that you would be losing 220-330 potency instead of getting it completely free.
- This has nothing to do with Dark Knight, but if this change were made then I feel like it would only be right to give Clemency an effect like "Your next cast of Holy Spirit or Holy Circle deals extra damage" to keep the DPS loss approximately fair.
While I'm definitely not in the camp that thinks there's some great DRK crisis when it comes to a self-heal, I do have to recognize that they are definitely missing a non-rotational heal that isn't coupled to their standard mitigation suite, and I could get behind something like this to give them a reasonable on-demand health bump in a way that doesn't warrant nerfing any of their existing skills to make room for incoming HP.