Since I came to McKinsey as an experienced hire, well after I completed my MBA, I've amassed years of experience both failing and then finally succeeding at case interviews. What changed? I finally started to use my own judgement and problem solving skills instead of just focusing on "what they want to hear."
So no more structure for the sake of structure, which obscured my own thinking, but rather first developing my own thoughts, and then structuring them in a way that allowed me to demonstrate my hypothesis efficiently and move quickly toward testing it, all while having a good conversation with the interviewer!
If this sounds like a compelling approach, please be in touch.