Tbh I don't really have any qualms about killing off Su De. We barely have any high stakes situations so far. Auntie death and Ai fridging are the only ones even close. He Gang ends up doing stuff that intentionally or unintentionally harms MC. Causing Aunties death, ragebaiting MC lmao, abusing Mei if you even consider that, attacking Ai if romanced, and now this. So when the time comes for us get revenge, all this has to pay off immensely. At the same time, I have doubts whether Su De can prove to be a good character in the long run. The only way a character can keep up relevance is if they are insanely strong or if they are plot relevant. She's neither. If this character goes nowhere, best utilize it now to the full extent. Besides, it may help develop tensions between the Su clan and the He clan as an overarching plot point.