I agree with most of your thoughts except the importance of gunslinger. Gunslinger is the best class for Hard Mode during the Atheon fight. When teleported you are able to quickly assist taking out any mobs that the relic holder is struggling with while still have a shot to kill an oracle. If you are not teleported you can efficiently use it to kill any supplicants that were delayed or just making it to the teleport as your team is coming through the game. Can find other areas where they are helpful but these are two areas that they surpass other classes. Killing oracles should mainly be left to raid weapons. Corrective measure makes it a walk in the park. I would say that skill of the player becomes a huge factor a well.