If you use DP when saurfang is in enrage at full runic please reroll other class that doesn't require you to think.
I know when you open your spellbook in holy you only have Divine Plea but other pallys have Avenging Wrath, Divine Ilumination (35% +healing if 2t10 pieces), things that mitigate the plea healing reduction, but it seems that this is to much for you.
And the crit paladin will have mana left before the fight is over if he/she has common sense and know how to manage cooldowns, MP5 pally doesn't have to think of that but the tank death is more likely if he's taking really high spike damage.