/facepalm - you linked the wrong priest.
The priest (I guess you intended to link?) has 2.7% uptime on Insanity.
Same priest - same raid - Garrosh - Same Talents - 5.44% uptime on Insanity.
Yes there are variables on each fight.
Do you really think that a difference of 2.74% is that big of a factor? Especially when you're also factoring the fact that protectors generally has more aoe and multi dotting elements in it than Garrosh in which you wouldn't want to Insanity because it is a dps loss - In fact you wouldn't use any level 45 talent with the exception of mindbender before the event happened.