Viability and optimality are concerns that come up often in raiding and PVP because in both settings players are very concerned with what works and what is best. Indeed, hunter theorycrafting and strategizing is driven chiefly by these concerns. However, viability and optimality do not have independent meanings. They always depend on context. Read on after the break for an explanation.
Let’s start with some definitions. Being viable means being sufficient for success at a given endeavor. Being optimal means being best-suited for success at a given endeavor. Viability is having enough to get the job done, optimality a condition of being best-suited for the job among the available options. You can be viable without being optimal, such as choosing to row as a way to get across the Atlantic. You can also be optimal without being viable, such as being the toughest and hardiest of the non-avian dinosaurs present at the end of the Cretaceous period.
To further illustrate the difference between the terms, let’s return to a beaten, run-over, burned and buried question, that of BM’s raid viability in WotLK. Was BM viable for normal mode raiding at the end of Wrath? Certainly. It could muster the required minimum of dps such that it was not being carried by others in normal modes. Was it optimal? Certainly not. It was far, far behind MM in dps, making it a long way from optimal. It could get the job done in normal modes but it was not the best spec to take to progression fights. And the tougher the fight (or the more hard-ass the raid leader), the closer the threshhold of viability approaches what is optimal, such that there is no difference for truly min-maxed comps, eliminating choice: “MM or you don’t raid.” Indeed, in Paragon’s estimation, the threshhold for viability can pass whatever is optimal so that there is no viable option for a class. This is what they felt to be the case for shamans on HM Ragnaros; shammies were just not useful enough compared to other classes.
Note that in the paragraph above I could not discuss viability and optimality without providing context. In the question of BM raid viability in Wrath, the ‘given endeavor’ is doing dps in normal modes and ‘sufficient success’ for viability is defined by not getting carried. Optimality is defined by the highest-possible hunter dps output in normal modes. Of course, if you apply different measures and standards for defining viability and optimality, you will get different conclusions. If your specified requirements for raiding are that the spec must to allow you to use your cool new spirit beast then there is only one viable spec for raiding (BM) and it is by default also the optimal spec. In this way, viability and optimality are conditional in their meaning. They depend on other parameters, other factors, to make sense and have definite meaning.
A consequence of this is that you want to avoid vagueness. You can ask whether SV is viable for PVP and get answers of “yes” and “no” with both answers being correct. SV is viable for low-level PVP but not high-level arenas. It is viable for defending nodes in rated BGs but is not optimal and is questionably even viable for the controlled burst and utility required in bringing down enemy flag carriers. The question of SV viability in PVP is simply too vague for any single answer to be appropriate. It either needs multiple answers or the question needs to be narrower in order for the intent of the questioner to be matched by the intent of the answerer.
There is also another problem, that of exceptions. MM was optimal back in ICC overall, but for Sindragosa? It was arguably worse than both SV and BM. BM could beat line of sight issues (and indeed even pet tank the boss) and SV could largely avoid the substantial pentalty to physical dps on the fight. There have been other somewhat recent exceptions as well like AoE fights between 4.0.6 and 4.1 where you felt obliged to be SV or Yogg phase 3 progression where BM was king. Such exceptions do not violate a spec’s condition of being, say, optimal for raiding overall, but they do identify another implicit condition. A spec is typically only viable or optimal for general endeavors like dps or pressure on average. There may be some fights or comps or opponents where a generally optimal spec is downright crippled or where it is simply exceeded by another spec.
In general, then, we can say that it helps to be clear when talking about viability and optimality. We should consider the viability/optimality of what, where, with who, when, with what exceptions, to what end and so on instead of leaving our questions vague. This is not to say that open-ended questions are bad, merely that they too should define their parameters to avoid misunderstanding: overall dps, overall pressure, etc. I suspect that hunter communication could avoid a lot of drama and disagreement if we were simply more careful with our words.