If you look closely, its not SP. Its priest in general.
The meta through all DF has been to simply put the priest that performs the best. Holy, Disc, or SP.
And the reason is : PI and Fortitude. And to a lesser degree as well MD and MS and disease dispel. I can deal with Fortitude being a priest thing. But the other forms of utility… I am amazed that they have not addressed that yet.
This is something that really bugs me about Blizzard.
They took literally 4 months to increase the CD of MD from 40s to 2 minutes. But they forgot what the problem was to begin with : It dispels Magic ! That was the issue !
Magic debuffs are supposed to be the Healer dispel mechanics. Allowing a DPS (and SP being the ONLY one capable to do that, AND being the only AoE dispel in the game) is unacceptable.
Aug/Evoker has a similar thing with bleeds. Bleeds are supposed to be the undispelable debuff. The one you had to heal through by force. Well turns out Evokers are special. And the only ones to be able to do that too.
And PI… well… I am baffled that PI is still in the state it is. Which party would not want a BL with a 2 minute CD? Its time that PI is turned to a priest only buff, and for the party turn it into a BL mechanic like everyone else.
And MS… Priest should not be the only class that can do this. If you can MS something and skip packs, so should a rogue with stealth, shroud, ect…
I am really confused how Blizzard thinks its acceptable that a Priest can solo 3 cages of BH by literally walking around the 1st area in BH… while a rogue… master assassin with stealth… cant…
And because none of this was changed for the WW, priest will continue to be meta in S1 of WW. Unless of course, you nerf SP damage so low, and healing throuput of Holy/Disc is so bad that you are forced to find a replacement.
But if any one of those 3 specs is marginally competitive… your stuck with a priest in your party.