Like dark prange said a WHM can not and should not rely on crit. It is nice when a cure 2 crits and heals the tank for 5k but as most skilled healers will tell you. You cure based on how much damage you expect the party member to take, not cure for 2k and hope for 4k.

In the event you need a lot of single target healing or you are low on mana you pop divine seal and all of your cures are now cure 2.

For WHM the priority goes Piety > Det > Spell > Crit

SCH prioritise Crit simply because their spells take advantage of crits. Adlo/Succor will place a shield that is twice as strong as the amount cured and the higher crit increases the likely hood of this happening.