Duty set and limited sets would work.

I quite like the idea of the duty set being slightly customizable though. Say 20 rigidly set actions, 5 actions with limited swapping and 3 or 4 totally free pick what you like slots.

Limited swapping is say 'this slot must be an AoE, but you can pick any of these 3 abilities with different secondary effects: one stuns, one poisons, one weakens.' That sort of thing.