This is a common misconception that stems from people who are coaching for BCG or BCG (with a proper background) that assume it must be the same for McKinsey as well, when, in fact, it is not. And it has been reiterated ad nauseam over the years.
At the core, McKinsey wants to see creative ideas communicated in a structured manner, the more exhaustive the better.
Your goal should be to come up with a tailored and creative answer that fits the question. The structure / brainstorming should - broadly speaking - follow these three characteristics:
In a McKinsey interview, you can take up to 5-7 minutes to present your structure, your qualification, and hypotheses. This is due to the interviewer-led format that McK employs. If your answer is not exhaustive enough, the interviewer will start drilling into your answer and ask if you have any other ideas. This usually happens if you
- haven't gone broad or deep enough
- did not explain your ideas well enough for them to stand out (again, you have time here)
The firm wants to see exhaustive and creative approaches to specific problems, which more often than not do not fit into the classic case interview frameworks that were en vogue 10 years ago...
Again, this only applies if everything you say
- adds value to the problem analysis
- is MECE
- is well qualified
- includes a detailed discussion of your hypotheses at the end
The difference in format and way of answering a question is the reason why I recommend preparing very differently for McK interviews vs. other consultancies.
If you want to read more about the specifics of the McK interview, check out this article: https://www.preplounge.com/en/mckinsey-interview