Honestly, they should just start over with Shadow Priest.
They keep reiterating, and add on more and more, and it just gets a nightmare to balance because they are probably the spec with the most actual buttons (other than Brewmaster, maybe).
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What flavour does it have?
10% extra damage?
It's not even a "personal buff". It's a stance that you have no reason to ever leave.
No one is saying to remove it but you might as well decouple it from the actual damage bonus bit and make it a purely cosmetic ability.