Shimmer is also a big part of this equation. I see players in here talking about how easy it is to interrupt or LoS GPyro, but Shimmer pretty much ensures that this will not happen against any melee, especially in BGs where most of the combat occurs in an open area with little to no means of breaking LoS.
Add in all the control and defenses like Blazing Barrier, Temporal Shield, Cauterize, and Ice Block and you have a spec that demands constant interrupts and CC which detracts from your ability to disrupt healers, which detracts from your ability to accomplish anything at all, but also leaves very little opportunity for aggressors to actually put them away.