As a hybrid class, I would prefer if AST was more hybrid based. Diurnal and Nocturnal should work like the bard songs, a stance that lasts 30 seconds on a 50 second cooldown or so. Have the ASTs alternate whether they are shielding or regening, and have their shields/regens stack with WHM/SCH. Make WHM and SCH's regens and shields more potent than ASTs, where AST doesn't shine in the potency department, but in the group buffs and ability to regen and shield in a fight. It would make AST more fun to play and it would help keep WHM/SCH both relevant and maintain their strengths.