Wallis' arc always came across to me as a redemption one after all the shit she did in the war on the Protagonist's homecountry. She was always trying to distance herself from her old teamates and her old habits. Even one of her first interactions with the Protagonist is trying to apologize.
So i don't really see this evil hardcore things other than outside of some bad endings. Also i would hardly call her story light. Instead i agree with
Tatsugaya, so far she is the most well written arc. Just a shame the devs in charge of the artwork didn't do a more detailed job (Claudia's route continues to be the best one when it comes to art variety).