No qq about pve gear in pvp during s6/s7? PvE gear in arena was a problem that was rampant during the entirety of Wrath of the Lich King.
http://www.wowhead.com/item=47059
Back then, Solace gave mp5, and back then you could stack both the normal version and heroic version of the trinket. Human priests when that was released were a nightmare to fight against, because their mana pool was limitless. You could then pair them with a holy paladin (who could also have double solace) and a warrior stacking as much armor pen through pve gear where he could and rule the 3s bracket with an iron fist.
A mage in an RMP could destroy people in a shatter combo with
http://www.wowhead.com/item=47316 without any assistance from the mage at all.
There is no issue currently about pve gear in pvp because right now pvp gear is tuned to a point where it is better than pve gear in the options of putting out damage and healing, along with reducing damage from other players, instead of it only being a survivability issue, and you could choose to wear pve gear for more damage only sacrificing damage reduction against players.