Killing Machine, you're killing me
Killing Machine is the source of a lot of discussion in the death knight community, with a large and vocal portion clamoring for a redesign. The biggest reason for this is that it's seen as making critical strike rating too superfluous for frost death knights. Since Killing Machine is a guaranteed critical strike, it means that the higher your critical strike chance, the more likely it is that the Killing Machine critical strike would have been a normal critical strike anyway, thus "wasting" a critical strike you could have had otherwise.
The biggest problem this causes is that it undervalues critical strike rating. It's the worst secondary stat for dual wielding frost death knight. It's 2nd best for 2-handed frost death knights, but only because mastery is also undervalued because Obliterate is physical damage only. Another, mostly separate issue is that despite 2-handed and dual wielding frost set up to prefer Frost Strike or Obliterate separately (with Soul Reaper getting in on the fun in the tier 15 4-piece bonus), it is almost never worth it to "save" a Killing Machine proc until you have your preferred strike up, but to spend it as soon as possible on whatever strike is available, because you might miss another Killing Machine proc down the line.
If Killing Machine is redesigned to address these issues, how might it be redesigned? One possibility is to take yet another cue from demonology warlocks. Demonology warlocks use Soul Fire in conjunction with Molten Core, a proc that makes the spell worth casting. In the case of Molten Core, however, a proc is not usually wasted because any new procs will stack on the old one. Using this mechanic could have a chance to solve the "saving" portion of Killing Machine because you could save it until your most effective strike was ready without worrying about wasting another proc. That leaves us with the critical strike issue, which Soul Fire has a solution for. Soul Fire is an automatic critical strike, but it does extra damage based on the warlock's critical strike chance. This means that even if a demonology warlock uses an auto-critical spell for a huge part of their rotation, critical strike chance doesn't feel like a waste to them because they're still getting extra damage out of it. For death knights, apply this logic to any strike that uses Killing Machine, and suddenly critical strike rating starts looking a lot less wasted.
Of course, the other question is whether this will solve anyone's problems. After all, high level demonology warlocks are still stacking tons of haste, just like frost death knights are now. So maybe where we should really be casting a weather eye is on haste.
Haste makes waste
Stacking haste has been the order of the day for frost DPS death knights for some time now. Part of this is because haste feeds into our rune regeneration, and we need a certain amount just to keep up. Compound this with various issues with the other two secondary stats, and haste becomes the easy stat of choice in most circumstances.
Of course, haste has problems of its own, most notably with the global cooldown cap, which makes haste that much less desirable (but not completely undesirable, mind you) once its hit. There's also the fact that this isn't a constant, easily express number, because the exact amount of haste that gets you there is dependent on your skill in keeping your priority system up and minimizing downtime to begin with. If redesigning mastery to affect Obliterate or making critical strike more useful for frost death knights proves too difficult, maybe nerfing haste is the answer.
The problem is, making haste weaker is a lot harder to figure out. Blizzard's made it pretty clear the rune regeneration talents are here to stay, and even if they don't use haste directly, haste still affects them in that the faster you can generate and dump runic power, the more often they'll proc. In addition, slowing everything down might affect the "feel" of frost DPS in a way that some may not like.
So what's the problem?
While the issues look clear to most players, one of the biggest things we need to consider is whether the developers will consider them problems. Ultimately, what may be the question to ask is if effectiveness is as important as variety. If we stack lots of haste, but still do good DPS, is anything lost? It may be effectively impossible to see every class and spec use all secondary stats equally. If DPS death knights do a lot of haste, but do good DPS, maybe we don't need that drastic of a redesign.
On the other hand, many people do like the meta-game of balancing stats on gear, and if the obvious choice is "cap hit and expertise, then reforge, gem, and gear for haste from now until the end of time," that's likely not completely compelling for them. Is Blizzard willing to tell those people to deal with it, or will we see an answer to those stat woes in patch 6.0? No matter which side you fall on, testing and providing solid math, especially on the patch 5.4 PTR is probably the best way to sway the argument we have, even if we don't see results until the next expansion.
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