The thing I've usually found helpful re: characterization is that especially for non-POV characters (i.e. everyone in Guardian, frex), there is a range of characterizations that do not contradict canon evidence. You don't have to pick the same one the rest of fandom does, and you can change according to the story you want to tell as well. (For instance, there's a very popular set of characterizations for Shen Wei that are heavily novel-based but which I find borderline OOC for the drama, that sort of thing.) Would embracing that vastness and writing multiple ficlets with maximally divergent takes on the characters help?