Well, I'm eager to hear what you think the candidate type of the best engineer is, why that type of candidate would fail to come up with a reasonable train of thought given the cited question in an interview, and how you select for that candidate type.

If questions like the one posted find a type of candidate who can think well under mild pressure, who can quickly brainstorm sensible approaches to technical problems, and who can communicate their ideas and reasoning to their peers, then that sounds like a pretty good outcome to me.