The problem with natural selection as pertaining to language is that the language may be great but die because the culture dies off or shrinks or gets assimilated. For example, I don't consider Spanish an efficient or well-designed language in the slightest, but it's very widely spoken because the Spanish are good at conquest. Ainu is very fascinating and possibly more efficient (in terms of syllables per second over syllables per bit of information). The Ainu didn't have much interest in expansion and got more or less assimilated by Japan. Doesn't mean the language got selected against, the _culture_ got selected against.

While language may have an effect on a culture's success, I suspect a culture has much more impact on a language's success. Natural selection is a terrible metric of “good ones” in that case.