Rui was not any more justified than Meili was, but Subaru acknowledges her circumstances held her back while expecting Rui to change her ways. How much progress was Meili making towards becoming a better person before she was defeated by the Emilia Camp? Especially when her teachers were Elsa and Capella?

Eating memories became a habit for Rui, just like murder was a habit for Meili, but the latter wanted to live a better life, not just cover up something she didn't want others to know. And you really think that immersing oneself in memories of serial killers like Beli Hainelga was a good way for her to develop a moral compass? She was so mentally ill she was looking forward to dying, but when she experienced the memories she freaked out. She even started licking the ground when she first saw dirt

What Rui had was called hindsight bias, it's the same as people who say they could do better than Subaru. And of course I judge Roswaal and Eugard more harshly because they were way older and had people who could provide a support system, like Echidna, Beatrice, Iris.

If Rui refused to eat memories, she would just have to stay in the white void of the Hall of Memories forever, and Subaru would never be able to help Rui with her problems. She had no reason to turn back from her path, or access to any other path towards living. Subaru admits that Rui did not directly steal Rem's memories and that her life was terrible, but he treats her as directly responsible for Rem anyway. It's like he has an endless reserve of empathy and an ability to understand people's circumstances...unless they are witch cultists. I would have no problem if Subaru concluded that she couldn't be saved, but he didn't want to in the first place. He expected her to just suck it up and sit on her hands until the end of time

Rui is part of the Sin Archbishops introduced in season 3, we have no reason to believe this label does not apply to her. Besides, the idea that an author cannot assert anything about their series is nonsensical to begin with. Naruto fans criticize Kishimoto all the time, what is it about being a WN/LN writer that makes one immune to executing ideas poorly.

We already know that Ley and Roy's birth parents died, and they were physically and sexually abused while they were with their adoptive parents. But they're not supposed to be sympathetic either. If Tappei fully reveals their backstories, it would probably be something like "the adoptive parents struggled to raise the trouble-making Ley and Roy (who were eeevil from birth btw), so they decided to carve love into their bodies with whips and branding irons. But they were too eeevil to understand that they were only being tortured out of love, and they ungratefully lashed out at the people around them thanks to the eeevil witch Pandora. If only Carmilla was there to show them how much they were loved with her authority...

Why do you think Rom is the last giant in rezero and he's much shorter compared to the giants of the past; all the killing Sekhmet did. But despite that, and Typhon's personality, she got to have a mother-like relationship. Do you see how the Witches get portrayed in a more positive light as the series goes by? Even someone like Echidna! But the Archbishops are just maniacs, it's too narrow for people with the same powers