I don't think he would be rejected, at least not for slowness of thought. If he were applying to YC with an idea he had thought about deeply, the answers to the questions in this simulation would be mere cache lookups, requiring negligible CPU. Only in the case of a cache miss would he have to think very much, and even then one or two cache misses probably wouldn't be enough to sink his application, especially considering how good the YC partners are at detecting deep intelligence.