Holy Priest - Levelling/Solo

I've started levelling my Holy Priest and am around level 61.

I was originally only levelling in dungeons where even as a healer I was coming top 2 damage. I just put this down to the horrible scaling in dungeons but recently my power has ramped way beyond where any of my other characters were at in terms of damage.

Most mobs die in a single holy fire with divine image talented and I can just round up 8-10 mobs and kill them in 2-3 hits.

The questions I had were:

Does this carry on into Midnight zones/world quests/delves at 80-89 and at 90?

Is this the case for all healer specs? When I tried discipline it was doing a *fraction* of the damage.

Thanks in advance.