So, I finally got around to actually finishing the game again with the new epilogue added in Patch 5, and honestly, I feel like it does go a long way to making Karlach's story work better, or at least it does for me. It doesn't really fix the fact that her quest in Act 3 feels very barebones compared to the rest of the origin characters'- Karlach's act 3 quest was basically to kill someone you were almost certainly going to kill anyway, and I don't think I'll ever understand why you would introduce the idea that Karlach's engine is a prototype of the ones the Steel Watch use and then do nothing with it- but the epilogue after the "Tav goes with Karlach to Avernus" ending felt like it at least addressed my 2 major problems with her ending: 1) that all her endings were horribly depressing, and 2) that is was absolutely baffling and frustrating that you never even tried to do anything to fix her engine. Well, now we have an epilogue that shows that Karlach and Tav are managing to survive in Avernus in spite of everything, and they even have a lead on a possible fix for the engine that Karlach sounds genuinely hopeful about. At least a few of the other characters even mention they haven't forgotten you, and are planning to try to help karlach escape Avernus if they can- Jahiera says something like "If we don't free you, it'll only be because you did it first" I think. I honestly thought it even felt quite hopeful.
I wrote it thousand times here and gladly I'll write it again
Her quest feels extremely unfinished in act 3 and all clues in the game shows you, that you should be able to fix her engine. But in actual state you can kill Damon and Gondians in act 3 and nobody cares, because most important characters for Karlach are useless to you, which is really sad, because I'm pretty sure combination of enriched infernal ore, Dammon, Gondians and upper city was the key to fix.
Patch 5 basically gives us hope, that somewhere off screen Tav and Karlach maybe do some steps to fix her, but who knows.
