Instead you see guilds stacking them and none of the classes that are supposed to be good at their one niche and aren't as good as a spec that fills EVERY niche. They need to pick one niche and let shadow have it, because it's absurd that they fill every niche with perfection and no downside. Because instead you see very few hunters, most groups will only run one Warrior and only for shout because their damage is pretty poor in every situation, one to no dps DKs, at most one Ret Pally. The numbers don't lie and because of a handful of overtuned dot classes everyone else suffers. Class design is in the worst place it's been since Vanilla when some specs were just not viable at all. The specs that have a single niche can't even perform in that niche roll because of specs like Shadow, Boomkin, Affliction, and Destro because they dominate ST, AoE, Multidot, and Burst AoE. The bottom line is, gut these classes across the board for roles that aren't their niche. If the niche is 2-3 target multidotting, than that's their niche and should not be doing as good or better than a spec who's niche is single target damage and doesn't have multidotting. Because the argument you're making for Shadow Priest works exactly the same way for the several specs that are missing right now.
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Unless it was changed within the last couple hours, the enrage was listed at 8 minutes 30 seconds at the beginning of progression and they were barely getting the bosses to 60% 4 minutes in. Regardless of why Limit is wiping, the problem stands that some specs just have it all and many specs have nothing.