Divine Reversal really acts as a special +4 armor for critical damage.
With armor +4 and Divine Reversal, you can theoretically survive an average 8 dice attack with no damage...
It's arguably better than that. In a recent match, my opponent had a terrible roll (I think he rolled 3 damage on 6 or 7 dice), my 1 armor cancelled 1 damage, the Divine Reversal cancelled the other 2 damage, and my mage healed 2 damage... so the net result was that when my opponent attacked me for 7 dice, my mage healed 2 damage.
"+4 armor that blocks crits" (analogous to armor +4 and 2x Veteran's Belt) wouldn't have have been as good!