Suggesting that a story should be changed, so it would have a good ending just because you prefer good endings is even more childish. I'm just really glad that you or someone with similar "great ideas" weren't there to advise Shakespeare, for example.
The story is for the storyteller to tell, listeners (readers) have a choice to follow or leave, if they don't like the story. You personally don't like dark stories with real depth and this story happens to be a dark one. Well, you have a freedom not to follow the story and leave, just like you have a freedom not to eat in a pizza bar if you prefer hot dogs. You don't have a right to demand that a pizza bar should stop making pizzas and start making hot dogs just because you prefer them. Your opinion is not an absolute that everyone should follow.
There are plenty of people who like the story the way it is, you have no right to judge them or the dev. There are plenty of great stories around that end really badly for the characters in them and people love them. Stories about happy people are boring as fuck. Put someone under pressure and the story becomes interesting, even if and especially if it ends badly for the characters.