Your tactic about first healers is wrong.
After many wipes cause of my own stupidity and lack of sleep i can easily tell you that the easiest way to do P1 is:
Fear the first set of healers, explode the imp somewhere at the side while still nuking the fuck out of her, depending on tries i got her anywhere from 58-65% before umbrals spawned, then you cleave everything down together with BC+OF and a few WWs.
Fearing the first set of healers means using her as a target and fearing right in the middle of them to have them run backwards, they will never do anything after that than right click you till you cleave them down.
Sometimes i even feared the fuming and simply run in circles around her till umbrals spawned and cleaved them down all together.
2nd healers if you actually do damage you will either push the phase around there or a few seconds after, you can ignore them and nuke her to push the phase, piercing howl them and cleave them down with BC+OF when the next imps spawn, the Umbral/Smoldering/Fusing combo, after that its just Piercing Howl everytime she jumps around and a fear along with a BC+OF combo and they are all dead, in pretty much every single try the second imps came at 50-51.5%, i simply pushed her and Piercing Howled them.
When i actually killed her my try was so perfect i had 95% HP left with not a single imp alive, but that was because i wiped so many times i learnt by heart what she will do at any moment, i think when i killed her she didnt even spawn the 5 imps combo cause i was too fast, around 1mil DPS while my previous tries with all sorts of tests and stuff i was wiping at 1-5% at 6 imps spawning.
All my tries after i read about the Omelet buff were below 10-5%, i only kept dying cause panic and stupidity.
There are a few things that make the fight easier that you need to learn:
Spiced Omelet is a must, 10% haste if you are undergeared is godly.
Fear every second set of healing imps, if 1 bugs out just kill it quickly.
Fuming imps can be ignored in P1, drop them somewhere at the side, maybe all together even better, but in P2 it can cost you a lot cause their slime slows you a lot, covers the ground of the Fel Lava effect and her purple effect making you take a ton of damage cause you cant see it at times.
What i found out to be good with fuming imps is to drop them at the corners, risky cause of rocks but doable, if you do it you have nothing to care for.
Did it with 895 equipped cause of Gronntooth with bracers+ belt but i did have death and glory which obviously once you get it the fight becomes that much easier cause you literally destroy the imps much faster.
What i learnt from the fight:
First smoldering imps cleaved down with BC+OF, i tried to leave one at 1-3% (depends how they spawn, this is easy or hard as fuck, you want them spawning at a bad place
) to refresh my War Machine.
Fear the first set of healers/explode fuming at the side while cleaving her or simply fear it too.
If fuming was feared just explode it after to get the War Machine buff and have even bigger burst.
Let the healers melee you, wait for Umblars, BC+OF everything, and nuke the hell out of her, simply just DPS over the shield and interrupt her.
Depending on your DPS/How well you did she is anywhere between 50-55% by then, most of my tries she was at 50-51% and i simply pushed her while the second imps healed her.
Piercing Howl second imps, dodge fire, nuke her asap, wait for imps, cleave them with BC+OF and a few WWs, burst her to 35% so she will teleport away, Piercing Howl imps.
Always watch out for Fuming imps in P2, its better to lose 2 seconds of DPSing to make sure it doesnt explode under her but near some corner than randomly die cause you get a 2mil combined damage in less tha 2 seconds cause you cant see grounds affects, Fel Lava in P2 hurts a lot too, not the boulder, the green circle coming from the room
ETc etc, its literally a learning and deciding when to do what that can make it easier.
BC+ OF should only be used at set of imps, everyone knows that, nowhere else, i wiped many times cause i panicked and used it at 5-10% to execute her only to get outplayed by shield, or shield + umbrals or anything of that short, simply dont, save BC+OF for imps.