Well..
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Priests, played correctly, have insane damage mitigation and recovery abilities. Every 15 seconds we can put up a shield that absorbs 1100 damage. My Renew spell is always going, which heals for 260 every couple seconds. I have an instant heal (Holy Nova) that does about 300-400 and damages anyone in the area for about 200. As an Undead priest I have a spell that does about 1k damage to an opponent and drains all that to me, as well. Every time I am crit, I recover 25% of that damage over 5 seconds also (so 1k crit = +250 life). With all these abilities combined, it's rare that I even need to use my 1.4 second cast time heal which does about 1.1k life.
Presumably it's the same for a Paladin or Shaman, played well. At least that is the approach I would take.
How much damage do you put out whilst keeping yourself so alive?