Too Random At Any Speed
This is, by far, the most common reason/argument that I see healers use in advising other healers to avoid critical strike. The syllogism goes:
- Critical strike is RNG
- RNG is bad
- Therefore, critical strike is bad
For those unaware of the term "RNG," it stands for "random number generator" and it's used as a proxy for anything in the game system that has an element of chance to it.
Obviously, the conclusion in (3) is correct if we accept the premises of (1) and (2). So let's take a look at each of these premises and see if they hold up to focused scrutiny. I'm going to examine them in reverse order.
RNG is bad
A very common belief is that healers depend on reliability. DPS can exist in the chaotic maelstrom that is RNG, but no player tasked with keeping the raid alive can afford the luxury of rolling dice.
Is that true, though? I was talking about this with a friend of mine who tanks (Schriko of Ebon Plaguebringer) and he provided the perfect comparison point: tank avoidance stats. Tanks are no less tasked with keeping the raid alive (they are, in many ways, the choke point of the raid's jug of health...lose that stopper--the tank dies--and the rest of the raid's health is going to come pouring out soon after) and should presumably also be concerned with "reliability" over all else, if reliability was the be-all and end-all for those who's failures mean the raid dies.
However, no tanking guide suggests ignoring dodge and parry, the two "RNG" avoidance stats for tanks. Acquiring a fairly significant amount of each is an important thing for tanks to do (well, not parry so much for bear tanks, for obvious reasons!), even long before they can reach full combat table coverage.
The reason is that raid encounters are fairly long combat encounters. A tank will be exposed to a huge number of boss or add swings over the course of the encounter. The larger the sample size (that is, the number of opportunities to dodge or parry) the lower the volatility of the randomness. That is to say, if you have a 20% chance to dodge and only one chance to dodge, you're looking at an 80% chance to get exactly zero benefit from that dodge chance. However, if you have a million chances to dodge, you have so many chances to dodge that you'll almost certainly see right around 20% of those million chances dodged which means you reduced your damage over those million swings by a fifth, or 20% (assuming, for this very basic example, that all the swings were equal in damage done).
The same holds true for healers or DPS. The more spells you cast, the more chances for any type of RNG (critical strike, weapon or trinket procs, etc) to stabilize around its numerical value and play out like a static value (as the 20% dodge plays out like a 20% damage decrease over a long combat).
Critical strike is RNG
At its base, critical strike is clearly RNG...the value denotes the chance for a heal (or damage, but I'm mostly focusing on healers here) of double the value.
That said, there are some things that you should keep in mind when considering critical strike as a healer.
The first thing is that some healing class-specs have a much, much greater number of opportunities to generate critical strikes. For example, let's look at holy priests. The majority of their healing comes from Prayer of Healing, Circle of Healing and (if the raid can spend a fairly large amount of time stacked up) Holy Word: Sanctuary.
Prayer of Healing can hit five players at a time. Circle of Healing can hit six, glyphed. Holy Word: Sanctuary can hit as many people as stand in it, so up to twenty five people in a raid setting.
That means that on each Prayer of Healing cast, you have five chances to critically heal, six chances with Circle of Healing and an indeterminate but high number of chances with Holy Word: Sanctuary (assuming you're making smart decisions about when to use it).
This stands starkly in contrast to a healer (or DPS) who casts lots of single-target spells. Those players can still generally count on critical strike largely smoothing out over an entire combat, but are more volatile from cast to cast. A holy priest really isn't, because their model is to cast, in essence, a ton of small heals...which greatly expands their sample size even on a per-cast basis. For a holy priest, it's not all-or-nothing even on a per-cast basis.
Returning to the tank avoidance stat analogy for a moment, if there were a type of tank that had the ability to break each boss swing into seven smaller pieces of damage, each of which could be independently dodged or parried, then dodge or parry would be even less volatile for the tank. That's the tanking equivalent of healers who cast a lot of area of effect (AoE) heals (even if such a tank doesn't currently exist...but maybe it should!).
This, of course, is not limited to holy priests. Restoration druids also have a lower volatility per cast, due in part to their AoE heal (Wild Growth) but also due to the fact that the ticks of nearly all heals-over-time (HoTs) can critically strike. HoTs, like AoE heals, also subscribe to the model of smaller but more numerous heals, which substantially reduces the volatility per cast.
Restoration shamans, with Chain Heal and Healing Rain, fall into this boat if they're primarily raid healing. Holy paladins have been pushed into this boat by the redesign of Holy Radiance (and its resultant synergy with Light of Dawn).
To be perfectly honest, discipline priests can end up here, too, if they find themselves spamming Prayer of Healing as raid healers, which is a fairly common style for discipline priests.
Let me clarify what I'm saying here. I am not remotely saying that critical strike is the best stat for each of these class-specs. What I am saying is that critical strike is not a poor choice due to its "unreliable RNG aspect." Critical strike tends to stabilize over raid encounters that aren't extremely short and spec or playstyle can even stabilize critical strike on a per-cast basis.
Looking at critical strike as an unreliable stat that makes healing raid encounters as chancy as rolling dice is simply the wrong way to approach analyzing our secondary stats and gearing.
There are, certainly, other factors to consider* in critical strike but unreliability is really not one of them.
The idea of this post is not to make a full review of critical strike as a stat, but rather to strenuously object to one of the most common philosophical arguments put forth within the healing community about critical strike.
*Factors To Consider Not Expanded On In This Post
- The cost, in rating, to get a percentage of the various secondary stat
- The talents that are affected by critical strike
- The spells you use that are affected by critical strike
- The effect on mana that the various secondary stats exert
- The value other secondary stats have to your spell usage (opportunity cost of critical strike)