Alright, just started watching Steven Universe. I'm 4 episodes in. That poor boy. All he wants is to be part of a family, and all three of the crystal gems are horrible mentors. Pearl likes to think of herself as responsible, but she cannot relate to Steven and is utterly failing to provide a system of structure that he can understand. Amethyst gets along with him, but she acts like she's the same age as him and can't provide him any of the guidance a kid needs. And Garnet is barely even trying. Greg is the best mentor figure Steven has in his life, and he's homeless with no future. At least he's actually taught Steven to have a positive outlook, but he's still not parent material.
That poor boy is getting wrapped up in big ideas of how he's going to save the day and have the perfect family, because the reality of his life is unbearable. I saw this show on the TV a few times when I was a kid and it bummed me out, but now that I'm a grownup I can see how traumatised that boy is and how badly he needs a responsible parental figure who can relate to him. All of the adults in his life suck! Watching this show is miserable, because I'm watching a kid who desperately needs a family be failed by the family he has.
I like traditionally grimdark settings like Warhammer 40k, but watching Steven Universe gives me the same feeling I imagine non-grimdark-fans must feel seeing a setting like 40k. Overbearing, unrelenting misery. It all sucks and it isn't getting better. On occasion 40k describes the life of civilians in that setting, how oppressed and abused they are by the fascist governments they live under. The fun of seeing evil soldiers who chose a life of violence killing each other fades away. Suddenly, we're seeing the perspective of the innocent. Their suffering. It's depressing and heartbreaking in the same way SU is.
SU is incredible. It gets so much better (AND 'worse'). You're not wrong! The writers are doing this on purpose, and they know exactly where they're taking the story.