mother of adamantium

But if a character deserved better and they don't get it, then that's unsatisfying bad fiction and I deserve better than being left annoyed/upset by a story's ending.

not really. if it is thematically coherent with the rest of the story and how it approaches finding meaning in actions and it works as a tragedy as well then it is not a writing issue. i only take “deserved better” seriously if they deserved better execution/the story left glaring untapped potential. otherwise i dont buy into “good people are entitled to rewards, because that is satisfying” bc i like when art proposes that that is not how it works and also it should not be what motivates us to be “good”. true heroism lies in the desire to try even despite of this reality, so it works if the reality is actually presented in the text. a character arc being incoherent and thematically unfulfilling is a different thing, and that is not about intradiegetic “deserving”