so... there is a pretty easy way to cheese this fight, you just need a small stockpile of chests and pile them up at the base of all 4 ladders, and at the top of the ladders... this will trigger a "cannot reach" effect when trying to use the ladders
the big grumbly machines aren't all that skilled at ranged combat. then its a slow grind to kill em all... instead of talking to gortash, begin the fight by shooting him.
if you have some grease, this can be another huge asset when it comes to making normally difficult fights very easy, as Larion didn't exactly prepare the NPCs to remove heavy armor to get out of the grease.
Honestly, Im not sure why we cannot reveal Gortash is a leader of the absolute to all and sundry to remove him from power and have a nice sizeable army to contest his steel watch. toss in that Zariel and Bane are NOT friends, and get the devil to help with the eradication of the steel watch... In theory, you just have to convince Zariel that if she doesn't deal with the steel watch, then she's siding with bane, and get other gods to intervene against her in Avernus if she doesn't comply... Zariel once served a forgotten god... she herself is not a god, but an archdevil, which means she's far inferior to the actual gods (comparable to the nightsong in actual power) Avernus is one of the 9 hells, so divine interventions there wouldn't necessarily cause the same kind of problems...
Personally, if It were me, I'd recruit Lord Belashyrra to handle the issue, as the Daelkyr is my favorite entity, far superior to a mere god, the daelkyr being the ones who created the gods to begin with... Belashyrra is the one who created the original mind flayer... and beholder... and mimic... you get the idea... the lord of Xoriat, the realm of madness, is rather insane himself. his contracts rarely make any sense, famously trading a whole country for the price of a cheese wheel... rule of theumbm, the more absurd it is, the more likely it is to work with him... and anything guaranteed to work, is guaranteed to fail. the only truth is that Belashyrra cannot be destroyed, only banished back to Xoriat. the same is true for all the daelkyr, as they are all primal embodiments of existance.
as long as there is thought, belashyrra lives. to kill Belashyrra you have to also kill everything that thinks, including the other daelkyr, like Orlassk the lord of stone... to kill him, the progeniter of all rocks and lands, well, all land has to go, from all realms. (that's just how unkillable a Daelkyr is)