Well one thing to remember when comparing Diurnal and Nocturnal. Yes shields are nice and if I heal for 2000 then it's a 2600 barrier. On the other hand Diurnal regen is 1100 a tick for 18s. So more healing without having to recast. Diurnal also gives AST a 5% Attack speed buff which is better for dps than a 5% healing buff that Nocturnal does. As much as we want Noct to be good paired with WHM it's really not.