You are looking for coders:
No I'm not - I'm very much looking for engineers in the mindset you describe. I just don't think your Lego robot question is a good tool for sniffing out that mindset. (For the simple reason that "muddled interview question" != "fuzzy real-world problem" - in fact there's a world of difference between the two).
But then again, we have a disconnect. Which is of course totally fine.