Why would anyone want a spec to be challenging tbh. I'm not saying any of the specs are challenging but wouldn't you want the specs to be as easy as possible. Im saying this as a heroic raider because most encounters especially spirit kings HC require your utmost attention on whats happening with the boss and in the raid, without someone having to fight with their character to get the best rotation/prioritization going. Fire "was" awesome, the prioritization was easy (for me atleast) and the DPS was high leaving me able to concentrate on the encounter 100%. I guess tho with enough practice any spec would become second nature to someone.
My 2 cents