I don't think framing it as Larian getting lazy or leaving her story unfinished is productive (or accurate!) The issue with Karlach's storyline is that she's tied to a lot of thematic points that no longer exist. Karlach outright tells you that she's going to live until she burns up, that she wants to spend it as happy as possible. That this is what ends up happening to her isn't a bad ending for her. It's only a bad ending because every other character can dodge their fate. It's most obvious with Gale, where Larian made it comically easy for him to just keep dodging his flaws and consequences. The problem of Karlach isn't that her ending is lazy or unfinished, it's that it feels tonally and structurally dissonant for one character to be given a bittersweet ending about accepting their situation and making peace with it when no other character has to. Like I said, I think she's a remnant of the earlier narrative. The story changed, her ending didn't.
Apparently, Karlach can also
volunteer to turn into a Mind Flayer when someone must do so near the ending, and figures she's happy existing as a Mind Flayer.
But that option didn't come up for me when she was present for the conversation.
While you make some agreeable points (mostly around the tone deafness), Karlach and Tav are pulled along by hope, Karlach wants to live more than anything, more than she wants to go out a hero, more than she wants to return to Avernus, and the solution (among many) to her problem is wafted under the player's nose. I can't understate how gutwrenching it is, to be told that the solution sits right in the Foundry, with the Gondians, only to not be able to do anything with it, not even discuss it with Zanner, Dammon, nothing. By the end of the game (and when you play as her), returning to Avernus is posed as the "best" ending, Tav (or Wyll) is going to go with her, keep her safe, continue to love her unconditionally. But we get no payoff, no epilogue to show us that our choice there mattered. As it stands, I don't think any of us find it LAZY, but definitely feel like it went unfinished due to time.
