I don't hate unhappy endings. What I hate is 6 different endings and not one of them is 'happy.'
I hate putting in 80 hours to clear the whole map, do every side quest, get every option in the final moments, and it all amounts to "pick who dies, but it's still probably everyone."
I feel like if you put all the work in to do absolutely everything there should be SOME positive reward for it.
I dunno, I think the mistake you are making is thinking it is a game to win rather than a story to experience.