In a highly lawful imperialist society, I argue monks can serve a purpose outside of wetworks. A closed community can pay special attention to the gods, showing extreme devotion to offset the perhaps more lackadaisical approach of some laymen.

Monks can also act sort of like priests, administering to the sick or beleaguered, making sure one’s faith does not waiver in the face of despair, full of advice and showing an example of a simple, devoted life a citizen can aspire to. The militaristic aspect of a monks training can have been started to defend the faithful and the monastery, maybe a way of life predating the empire when communities were centered around the places of worship.

This would operate in contrast to your description of the clerics in this world, which do indeed sound like they could purge the xenos, the mutant, and the heretic. The cleric represents maybe the military industrial complex that evolved with imperial expansion.