Instead of having them being at war with themselves over a caste system, let the Shura be at peace with the violence that lives inside of them, they don't understand the concepts of war or hatred. Eating lesser creatures isn't war, its just the way things are. The strong consume the weak, the weak consume the dead. War is strange, the fish dont fight among themselves, the whales don't and neither do the Shura. Mating, eating yes, but not conflict for the purpose of dominance