Death Coil’s healing sucks.
For example in current Season TTW full honor gear I have 18,346,640 HP in PvP, Death Coil heals me for 654,537 or 3.56% of my HP. Meanwhile a minimum Death Strike heal is 2,054,823 HP or 11.2% of my HP. This means that even during Lichborne you would want to spam Death Strike (and this is without considering Blood Forged Armor). For Death Coil to at least break even with Death Strike we would need to multiply it’s healing by 3.14x (or 2.69x if you wanted to break even with runic power cost per hp healed). Death Coil would at least hold some value then but would probably still suck in many cases because of no Blood Forged Armor, never mind the fact you can only self heal with death Coil during Lichborne, so it should really feel like a powerup not just break even.
Okay, so if Death Coil healing sucks during Lichborne is it at least good at healing up our dedicated ghoul minion, Timmy? Short answer is no, it’s also terrible at that. My Timmy has about 15,594,000 HP in PvP. My 654,537 Death Coil heal is only 4.20% (lol). So lets pretend for a second that Timmy has 1% hp and I want to heal him to full, I would need 24 Death Coils, if I had unlimited runic power that would take between 24 and 36 seconds depending on haste, the cooldown to summon a new ghoul is only 30 seconds. It is more efficient to dismiss and resummon Timmy than it is to actually heal him even in this insane hypothetical where I have unlimited runic power. Because you are wasting a resource you don’t need to (because raise dead CD is so short) Death Coil heals on your pet should feel rather substantial, somewhere between 20% to 35% which means I believe it should be healing somewhere roughly around 5x to 8x.
So is it all bad? Well not quite, I started a remix Death Knight the other day and during the first Dalaran quest I was losing HP with no decent way to get it back except via Lichborne + Death Coil. At level 10 it was healing me for around 80-100% of my HP so I could basically non stop fight just by managing Lichborne, it was great and I feel like it captured the relentless spirit of DK play. Death Coil Healing just fails to keep up as you level, by around level 40 (ilvl ~170) Death Coil stopped being more efficient than Death Strike.
Now as an Unholy Death Knight you can really notice how Death Coil’s Healing fails to keep up with as you get more multipliers on Death Coil’s damage, so part of me thought we should just make the unholy talents (and mastery) also affect the healing, but upon more reflection I think it’s a really short sighted solution. Going into Midnight we no longer have a damage reduction for Lichborne, so if the cooldown is suppose to remain viable for Frost and Blood then they should get just as much healing as Unholy gets, heck if anything Blood should probably get more than the dps specs as it has a larger health pool and a more competitive Death Strike.
I think the best solution is to increase the total Healing of Death Coil by 6x, but do so in a way that scales healing as we level. I would make it so that it heals for the same amount it does right now at level 10, but linearly scales up to 6x as much by the time we get to level cap. Furthermore I would consider adding another Death Coil healing increase to blood as a passive you get while leveling, or attach it to an existing passive you get while leveling.
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TLDR: Make Death Coil Heal 6x as strong.