Karlach was a very late addition to the game. She was not available as a companion in the EA, nor was she visible in any promotional artwork (meaning they didn't even envision her as a companion at the start of development). Hell, her appearance was only finalized a few weeks before launch. Given how little time they had to develop her, they went with the simplest story possible: collect 2 items and die, lol. I don't think any writer is happy with that "story". They simply wrote what they could in the limited time they had. Keep in mind that the character needed to be integrated into existing quests, so the writers' hands were tied. They almost certainly weren't allowed to write new quests as the dev team wouldn't have time to implement them.
Well, if Larians care that much about quality of their game as they claim they should have cut Karlach from the game on release entirely to be added in later dlcs or expansion, rather than leave this half assed origin companion with embarrasingly short and boring questline.
