Dont know about others, but im bad with current ending because:
1 - There no quest for here at all. Everyone has a quest, even Halsin have a quest, but Karlach not!
2 - There plenty of possibilities to fix her engine: Gondians, Dammon, Gods, Devils deals, Elmister, True Resurrect (in game canon one, just give me opportunity kill Gale and safe this scroll canonically).
3 - No matter what you do your action have ZERO affect on her story. Its companion without a choice in a game that`s all about choice in a genre that all about choice, it`s just wrong. Like when shooter give you a boss that you must kill without guns - if game not working on it hardly and build all around it it`ll be wrong and will don`t work well.
4 - All companions can have a happy end, some even a perfect Disney happy end (like Gale), but Karlach don`t... Her problem even doesn`t so horrible as Gale problem!


Justice for Karlach!