The numbers don't lie
Complex math problems, like DPS balance and spec performance, can be difficult to solve. Complex math problems without all of the right numbers are impossible. With millions of raiders playing on hundreds of servers, I can't imagine that more than 10% of all raid parses are uploaded to World of Logs. We can easily find top subtlety parses comparing favorably with top combat and assassination parses, so it's clearly not a mechanics issue that's holding subtlety back. The class is mechanically capable of keeping up with both of its rival specs.
The issue is that there are so few talented and geared subtlety rogues playing in major guilds and a plethora of PvP rogues with more resilience than hit rating trying to score some PvE loot. In one of the DPS Bot ranking charts, there were several parses with subtlety rogues doing literally zero damage. If the world's top rogues all switched to subtlety today, we'd be seeing a very different picture. Subtlety's problems lie in the fact that its PvE representatives are few and far between, and that it doesn't have any mechanical gimmicks that force rogues to keep a sub build around.
Subtlety's flavor is gone
Subtlety's flavor was parted out and sold at auction in Mists. The spec's defining characteristics, like Shadowstep, Preparation, and Cheat Death, were all made freely available to all rogues. Combat, even after the upcoming Blade Flurry nerf, is still the king of cleave. Assassination rogues can deal massive AoE damage via Deadly Poison and their natural tendency to stack mastery rating. Subtlety rogues have zero cleave and awful AoE capabilities. If you can only have two specs at a time, why would you roll into a raid with subtlety at all?
Every rogue is picking up combat and assassination for PvE. You play assassination most of the time, simply because it's performing well and it's does great against trash. You play combat any time the fight calls for it, which is a handful of encounters per tier. Blizzard is already nerfing Blade Flurry and talking about buffing combat's AoE to make it more competitive with assassination. Why is subtlety getting left out here? Combat is always going to have flavor and a reason for existing if Blade Flurry is still exclusive.
Repairing subtlety's image
There are zero reasons to play a subtlety rogue in PvE today. The spec has no defining characteristics, no flavor, no increased survivability, no increased mobility, and no utility. Every single piece of flavor has been extracted and transformed into talents. You get three moves for picking subtlety at the talent tree screen: Hemorrhage, Backstab, and occasionally Ambush. Congratulations, you're now the least effective rogue in your raid.
If the 50% damage bonus from Sanguinary Vein affected Crimson Tempest, are we even having this conversation? Subtlety's burst AoE capabilities would instantly spike to the top of the pile. Let assassination's slow poison method still keep the sustained AoE crowd, but give me a reason to keep subtlety around. If subtlety rogues deal equal single-target damage but don't have a defining characteristic, their population (and thus performance) numbers are going to continue to be at the bottom of the barrel.
Subtlety's stolen identity
A 4% buff to Sanguinary Vein is not Blizzard's grand attempt to fix subtlety. I have a hard time believing someone said "I think 4% ought to do it" and then put it in the patch notes. The buff is designed to get rogues trying subtlety again. The buff is designed to give current subtlety rogues some reassurance that they're not completely crazy for using the spec less travelled. The buff is designed to let us know that subtlety isn't completely dead.
I am not going to pick up subtlety unless it meets one of two criteria: significant single-target dominance (and I'm talking a 10% or more DPS advantage) or strategic raid utility (cleave, AoE, or otherwise). Assassination has ruled AoE for years. Combat has been the cleave king for WoW's entire lifetime. Subtlety used to be the survivability spec. You played sub when you needed to stay alive or soak nasty ability. Subtlety's PvE identity is gone, and I don't think a 4% buff is going to bring it back.
Sneak in every Wednesday for our Mogu'shan Vaults guide, a deep-dive into the world of rogue rotations -- and of course, all the basics in our guide to a raid-ready rogue.