The damage over time of Emperor of Corpses is way too high - just look at the 1:30 timestamp of this YT:
If DoT kills you instantly BEFORE an animation appears, then something is wrong with it. And basically it is no longer DoT, just instant kill damage. (I have all res maxed out, over 75%)
And yes - I know, if I only had 60,000 Ward - I probably wouldn’t be dead, but Ward is a separate issue in this game
You aren’t supposed to get hit by his breath, especially not with only 1500 HP.
You were standing directly in front of him, making no effort to move until the last second, as he did the very big windup for his breath attack. There’s an at most half second gap between when you got tagged by it and when the VFX actually appear, yeah, but you were going to die whether the VFX started at the same time as the damage or not. You stopped moving right in his face, right as he was gearing up to puke fire at you, and you locked yourself into your trap throwing animation so you couldn’t Shift.
You got greedy because the boss was almost dead, and stopped paying attention to what he was doing until it was too late. Getting killed by things you’re not supposed to get hit by is not a “damage is too high” problem, it’s a playing-the-game problem.