Here's I would fix all cheese in the raid.
I'd make an actual hard mode without the bullshit no-respawn thing. That's lame and is simply frustrating because knowing when it's safe to revive someone is a viable technique to learn and to master.
The oracles would come in different colors. Upon the first wave of oracles, whoever destroys an oracle, they can only destroy an oracle of that same color from that point on. The player would see this as a buff/debuff on their screen (Azure Resonance/Gold Resonance/Scarlet Resonance/Emerald Resonance/etc). The colors would appear on random oracles, so folks would have to call out where a color is and have the assigned person destroy it ASAP. Killing the wrong oracle would mark everyone.
The templar fight would implement this same mechanic with the same rules. Except now if at least two Detain bubbles touch, the people in said bubbles die.
For the Gatekeeper part, only Praetorians would spawn in replacement of the Goblins and Hobgoblins when protecting the portal circles? Why? Because fuck you that's why. This is heroic so you better damn well be a hero.
For Atheon, have him randomly pick three dudes to go back/forward in time. The detain bubble bullshit would remain the same as above. Also, Supplicants would spawn in waves randomly from where all enemies spawn back when you were fighting the Gatekeepers. I'd also reduce the Time's Vengeance buff to 15-20 seconds. Make Atheon's enrage timer 4 minutes and 30 seconds. When he enrages, Supplicants begin swarming en masse like they already do, and to be a real bastard, I'd have Supplicants spawn in the portals.
This is how you git gud
I don't know if I'd agree to everything specifically, but I do wish hard mode actually had new mechanics without the difficulty boiling down to unlucky deaths where sunsingers easy-mode self-revive looks like some overpowered god ability when in reality it's just a crutch for people being bad.
Oh snap I forgot about that. Thanks for reminding me.
No problem, I love Warriors games. C: