Not condoning Sandrone's actions. She's still a fatui harbinger, who tried to infiltrate Natlan, and is working alongside other villains like Childe who tried to drown Liyue, Signora who caused a civil war in Inazuma, Arlecchino who runs an orphanage of child soldiers >!though they can leave if they want, with no consequences.!<

Valid criticism can be pointed at the writing for the traveler for not properly confronting these characters on their actions, but argument can be made on the traveler's morality. But it's invalid to say, that these characters are "redeemed" rather, they are not morality black and white. Hoyo has a patten of writing gray morals when dealing with characters with large complex roles in the story, while smaller characters are sometimes written black and white.

Reminder in the last act of Natlan, Sandrone tried to kidnapped Ineffa. But beyond that, we don't know, what she wanted with her, or how she would have treated her if she succeeded. Even the fatui involved, who were working under her orders, were also written with gray morals, with them apologising for the spy's wife getting hurt. Basically what I'm saying is, people need to analyse the characters and writing as a whole before making grand sweeping statements like Hoyo is redeeming villains, or the traveler is a hypocrite hero.

Jenck, the character who got his tongue cut: https://genshin-impact.fandom.com/wiki/Jenck

The world quest in question: https://genshin-impact.fandom.com/wiki/Questioning_Melusine_and_Answering_Machine
Bad person does bad thing to bad person.