I liked Agent Kallus' redemption arc in Rebels. They set it up perfectly with him being a competent officer and a true believer in the empire, and it was in large part that competence that led to his disillusionment as all the various fuck ups, corruption, and deliberate cruelty [as opposed to ruthlessness in pursuit of actual purpose] were as much a factor in him switching sides as the warmth and decency of the Rebels themselves. Neither factor alone could have made him turn, but seeing the empire's wastefulness and the Rebels honorableness both combined into making him be the better person.