This "highly specific scenario" is a big part of Mythic+ and you make it sound as if we had stronger single target damage and outclassed others in boss fights to compensate which we don't.
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I doubt that. Best I managed in Unholy so far was around 20k peak aoe dps. I have seen several other classes pull either this much dps consistently on every aoe pack or 2-3 times as much in certain situations.