Let me clarify this 1 hit issue. On Hard mode it's a 1 hit if all fusions land and if the oracle literally just spawned 1 second ago. Shooting it as soon as it spawns can 1 shot them. Other than that it's a 2-3 hits on oracles. With 3 hits being more common. For some reason when oracles spawn they have low health or are not formed completely hence the 1 shot occasion.