https://www.warcraftlogs.com/statist...y=4&dataset=90
Go through every boss. The higher percentile, the worse the relative performance gets. You can check Mythic as well, but that data is still very light/non-existent for many fights. (the early returns are...not good). From a pure log performance perspective, Frost is currently one of the best specs in the game while Unholy is one of the worst. Sure, maybe all the good players are just playing Frost and that skews the numbers, but that's always been a specious argument. Most players flocked to Frost and continue to play it for a reason: it's flat out better in nearly every scenario, on top of being easier to play. Hell, check the max parses. Unholy is at or near the bottom on damn near every fight, sometimes embarrassingly behind even the 2nd worst spec. Star Auger and Krosus, two of the more DPS-intensive fights in NH, are particularly hilarious in that regard.
Frost is better than Unholy on every fight, from anywhere to 1% (Skorpyron
) to nearly 15% on the more ST fights. Unholy single target damage is downright abysmal, and its mediocre cleave/aoe does not bridge the gap. The situation doesn't look to be getting better with gear, either.
It's fine if UH is a bit weaker on either ST or AOE than other melee specs, but to be mediocre at AOE and terrible at ST isn't a tenable position. In best case scenario fights with sustained cleave or AOE, UH is middle of the pack.
I love the spec and it has a ton of potential game play-wise, but the rotation and resource spend/use dynamic isn't quite there. To make matters worse, Unholy requires more effort than most specs in the game to play optimally. Not saying its difficult, but that's just a cherry on the shit sundae that is UH performance.
I do like some of the suggestions I've seen here lately in order to improve the spec beyond just numbers-wise. Things like allowing DC to consume more RP to do more damage, removing the rune cost of SR, eliminating some of the wound proc RNG - all are fairly simple changes that would really improve quality of life.