Yeah, you pretty much hit the nail on the head, I think. It doesn't ruin the game for me, but it does make one very great character's story end in a very unsatisfying way, and 90% of it is down to the fact it feels like you just don't try at all to do anything to help Karlach. You deliver 2 pieces of infernal iron, get told she's dying, and immediately just give up. There's never even an option to *try* to do anything, and considering the other companion quests can involve stuff like invading a devil's stronghold in Hell to steal an immensely powerful artefact, fighting an ancient vampire and his whole coven, fighting an entire temple of the followers of an evil god, and so on.... it's just incredibly jarring that there's never any point where you can even try to help Karlach out.
