I felt like developing her so much and and the actual impact of her character and the relationship for Wade made her transition into a Lady Death composite so much more meaningful. It’s not as though she’s gone from the movie once she dies. Hell, Wade almost allows himself to, rather uncomfortably, die of super-cancer. It’s harrowing to watch and - well, the Lady Death stuff was incredibly well handled.
You might have a point about Russell being by the numbers, but I think the stuff they wrote for him and Denison’s acting more than carried it out. The kid can act the part of scared lashing-out wannabe very well.