The problem with a comparison of idiomatic solutions is that they rely in different degrees on what's in their libraries. IIRC the shootout tries to avoid this by comparing similar solutions using the same algorithm that are actually implemented with the interpreter/compiler in question. IMHO that's the more sensible way to do this.
Perhaps that concern is eliminated with good test programs? As an extreme example, if I wanted to compare how different languages do array slicing it's meaningless to force python to implement array slicing without the [:] operator. But then this whole test program is meaningless anyway.
You're right that there's a lot of nuance here, and perhaps there's no better solution. It's not even clear to me if there's a meaningful question to be answered. "This ocean's warmer than that one? What part? In summer or winter? Did you measure near a blue whale's fart?"
