Rebels could be good because it isn’t anime.
Let me pose a question: Do you think that once something is an anime, it automatically sucks. And for what reasons?
It doesn’t automatically suck, but no good anime has ever been made. I suppose it’s possible a good one will be made someday, but history is not on the side of that happening.
Answer honestly: Why it so categorically bad? Do not dodge this question, I will be persistent in trying to get an answer.