I'm posting this because Reddit user redgoesfaster really brought a point in Nom's post on there:
"Mizora tells wyll if he chooses freedom his father dies - we still save his father after he chooses freedom
The emperor says we cannot free Orpheus because he will kill us - Orpheus does not kill us after we free him and is actually pretty chill
Ethel says we cannot save the child if we kill her - we kill her and save the child
Orin says she will kill our party member if we don't kill Gortash and hurry to her - we spend several weeks at a circus with an angry djinn and still save our companion without fighting Gortash
Mystra/Elminster AND Gale say Gale has to sacrifice himself to destroy the elder brain - we destroy the elder brain with Gale very much in tact
Omeluum says we can't save him and have to go for Ravengard - we save him and Ravengard (he even has a great ability making saving Ravengard easier)
Florrick insists all hope is lost and she has to die in her cell - we very easily convince her she's wrong and rescue her
There are a plethora of times through the game we are told something and prove it to be false. The fact that all the "Karlach's ending makes sense" stans parade what Dammon says (again a self defined APPRENTICE infernal smith) as absolute fact is such a silly hill to die on lol. That's not even going into the 5000 ways in dnd canon that we could save her. The fact is Karlach's ending just doesn't make sense, they could make it make sense and still insist on their shoehorned tragedy because angst=good story telling. But instead they lock it behind "one guy said this is how it have to be so this is how it have to be"."
Now add to this that said apprentice infernal smith later in Act 3 figures out a way to do it, to fix it, lines recorded and all but never made it into the released game - most likely because whatever we'd need for him to help her was actually in either Upper City or Avernus cut content - and you realise that this "we cannot fix her/can't fix her outside of Avernus" is very much bs also.
It's an active choice by Larian devs to pluck that out for whatever reason and it's the most jarring thing there is. Simply because we can do the opposite of what we're told we can, if we try hard enough. The devs said themselves, if players have a thought as to how to solve something and it's unconventional (see, crate stacking your way to 10th floor), it will still exist in the game.
Karlach's no engine fix is, once again, pure bullshit and an active dev choice to cut something that should have been there. For whatever (stupid Imho) opinion.
