I'd argue that if you can't tell the difference between a good system design and a bad system design other than "see if it works," you shouldn't be in a positio

I'd argue that if you can't tell the difference between a good system design and a bad system design other than "see if it works," you shouldn't be in a position to be giving system design interviews. The idea isn't to get a working system, it's to see how the candidate approaches a system design. If it's a problem you know how to solve and you can't see problems with their approach, they're probably at least as good at it as you are.