Hmmmm...how did you get your math? On tanks the numbers are totally less. On a 19000K HP tank, which is what ilv200 DK and Pally should be, 30% would heal 5700, EVERYTIME, cleric stance or not, diseased or not.

901 Healing Lustrate right now heals about 4K average, I just popped 12 lustrates in a row on this AFK guy and not a single one crit.