That's an interesting take considering those small moments are pretty much all she has. She doesn't have a fleshed-out storyline, entire zones, whole chapters, and large subplots dedicated to her like the others do. If you take that away from her, what does she have left?
Following the arc that I outlined, finding the cure takes a whole different meaning. Survival and living are two different concepts. Now Karlach doesn't want to survive, she wants to live a fulfilling life. Because she didn't envision it before, she was ready to die, surviving only as far as it allowed her to accomplish her final goals. It was the same for everyone else. They each had their own goals that they wished to survive long enough to accomplish. None of them, however, needed to be convinced that their life was worth living. Only Karlach. That's what her story is about.
I wasn't talking about taking away small moments, but about giving other characters the attention they deserve (hello Wyll, hello Minthara apparently) and maybe about not forcefully taking attention away from them in order to focus it on Karlach, no matter if you care or not. There is a whole thread here about how you are forced to tend to Karlach's engine exploding at the dock but are not allowed to follow Spawn Astarion instead, who has to leave the scene while the other characters are joking about his plight, even if he maybe is your partner.
As for your last point, there is this majorly depressed wizard, who in Act 3 still does not completely believe that he as a human being is worth very much, thinks that the world would be better off without him and that nobody but his cat - and maybe the PC - care about him. But I guess he talks too much and there is not much attention forced on his situation, so it's maybe easy to miss? Gale really has to be convinced that his life is worth living and what there can be to life, but for him this is merely a jumping off point for his final dilemma. (And he also doesn't have a dungeon, he has a corner in a bookstore. Not complaining, I love the vault. Just saying.)
I would also deny that Karlach needs to be convinced that her life is worth living, she totally seems to believe that it is. Otherwise the conflict you pointed out, wouldn't even be a conflict. Her thing in the end seems to boil down to not wanting to be alone. She says something along the lines of "when you are with someone you love, it's all a little easier" during the epilogue. There isn't a change in her attitude (being alone was from the start one of the things she hated most about Avernus) there is a change in circumstances, Wyll or Wyll and the PC go a long with her. If you had made her the offer to go along with her earlier, she'd probably would have taken it too. (Or can you? I don't even know anymore. I think I clicked on all hell-adjacent dialogue lines at least once and they have all become muddled up. - I think you can suggest she could stay with Hope?)
Also, this forum desperately needs to visit Dammon .... ^^
