Heres what I think killed Steven Universe. Sugars entire philosophy on storytelling is terrible for one. The goal of storytelling isnt to do shit you find romantic like "oh its liek dreams guise and I'll show peopl my imaginashun and it'll be part of yours!" its specifically attempting to create something engaging and great for people to enjoy to express something. But Sugars entire philosophy on this is terrible, because it doesnt seem like she can say no to anything.
Think about it, she cant tell her artists to draw anyone the same height or age because she doesnt wanna mess with their style. But thats horseshit, its just the same style inconsistant. They arent drawing them in different ways. And even then, we dont want THEIR stories and art. We want the one that was being written at the start. If I made a Youtube channel and got 1 million subscribers and sold it to someone else, they wouldnt keep watching it, because its not what they signed up for.
The writing is literally fanfiction. Noone develops or improves because if they ever actually did they wouldnt have something to angst over. No progression to the main plot to focus on innocuous mundane bullshit and tell stories about whatever sidecharacters they want because Sugar cant focus on anything or say no to anything.
But letting people do whatever they want just makes your show inconsistant, it completely slows down the plot, people completely veer of track, they get lazy because they can, and nothing is correcting them. Then when they finally feel like getting around to doing something, theres basically no build up at all. Not to mention losing any sense of an actual vision of where things are supposed to go, beyond what everyone already expects.
Sugar wont make anyone do anything for any reason. She wont focus on the plot, she wont correct anyone, she wont correct mistakes. And the writing and art has gotten lazy as hell. The endings retconning everything sad and everyone makes up. End of.