"It's very lame to have a one note villain who is just evil just for the sake of being evil. It's also not very realistic."
Shasta, Dolores Umbridge from Harry Potter was one of the most popularly hated villains in the series, even surpassing Voldemort in some areas. In the novels and books, she was evil just for the sake of being evil. Even Voldemort, who was given a sympathetic backstory, embraced evil just for the sake of evil.
With Jadis, it actually showed in the hall of statues that the rulers in the beginning of the room had faces that were described as nice. The faces as Polly and Digory moved down the hall became sterner but still happy, then started to become cruel while still keeping a somewhat happy expression. Eventually, the happy faces were gone and despairing and cruel faces were on the statues. Jadis' face was described as fierce yet prideful. But I would ask regarding Jadis how to give her redeeming qualities when she committed complete genocide on her planet and tried to kill Aunt Letty simply for not kneeling in front of her and speaking ill of Jadis when Jadis was a guest in her house.
As for being realistic, there are real life people who are evil just for the sake of being evil. They may have somewhat sympathetic backgrounds, but their actions go far beyond their pasts and into pure evil.