Except you can change her fate and you can convince her to keep fighting, hell, there's entire cutscene at the end added specifically because players requested it, how do you want even more than that? And we have quite plenty of quality time with Karlach across the acts, obviously it could be more but this is rpg not dating simulator. I can agree that her questline is a bit shorter than some companions but it's still great and nicely ties to the main story with Gortash, makes her feel like a main character, other companions don't have that. As for solutions, well, Dammon tried and failed, we didn't find anything useful with Gortash so yeah, we're kinda out of options. Obviously you can try some gymnastics with DnD mechanics, but with ridiculous options the game offers it would be horrible for the narration because basically everything could be solved with Wish, some divine intervention or whatever so i'm happy Larian sticked to their story. It's a bit similar to the Cyberpunk story, we try many different solutions and fail, that doesn't mean the story isn't rewarding or great. I also don't know why people bring up Wyll constantly, his story is also great so I don't know what more you'd like for him, Halsin for example doesn't have his own dungeon but is still good character
You can change her fate only at the very end (or if you decide to turn her into a mindflayer). She doesn't need much convincing to fight with you until the end. That's what she wanted to do before and after her confrontation with Gortash. You have to play your cards very badly in order for her to leave your party. The only thing she needs convincing of is whether to go back to Avernus or not, which happens at the end.
That Avernus cutscene is not what players requested. What we've been requesting from the start was a way to fix her. That scene was added because, before that, the Avernus choice literally ended with a cut to black, meaning a cutscene should've been there but was missing. That they added it in such a short amount of time is awesome but it's not what most of us were talking about in our feedback.
By quality time, I don't mean dating. I mean having heart-to-heart moments, her spending time with people that she knows, and getting some actual closure. She even suggests going out to dinner with a friend in the city. Why not do that? The scavenger hunt just wastes the time she could've spent doing that instead.
Her questline is very, very short. Especially when you compare it to Astarion, Shadowheart, or Lae'zel.
Both Shadowheart and Lae'zel's questlines were tailor-made for the main story. Lae'zel's creche subplot is a major part of Act 1, while Act 2 is pretty much Shadowheart's turf. Karlach's only meaningful connection to the main story is Gortash, and that ends quickly. Just look at this post to get an idea of how staggering the difference is.
Hard to say she feels like an MC when you can ignore her entire questline and nothing much changes.
Astarion has more of a sidequest going, but it's fully fleshed out. Gale doesn't get much out of the main story, but he has a good thing going for him in his own right (if a bit rushed). Wyll on the other hand feels sidelined by the Emperor in his own story. Halsin isn't an origin character, so not having any dedicated content for him is to be expected.
Back to Karlach -- you yourself said it. We try (once!) with Dammon. He tells us that if he's worth his salt, he'd have figured something out by the next time we meet. Yet, when we meet him again he says we're out of luck. Not worth his salt, I guess? That's a very abrupt and disappointing development. There's not even an attempt at something new here.
As for Gortash, he's directly connected to the quest to save the Gondians. They are infernal engine mechanics who built the Steel Watch (which drop enriched infernal iron). Saving them is infamously frustrating to do and could've yielded a hard-won solution for Karlach, but we're not allowed to pursue that path.
Cyberpunk's story is one of tragedy from the get-go. You also try and fail multiple times, not just once, and even then if you play your cards right, you can get a hopeful open ending where you're free from the shackles that bound you to Night City and given a chance to save yourself.
