Article notes that info transmission is roughly the same for all languages. I wonder if this is the case for all subgroups? Do New Yorkers convey information more quickly than Vermonters?
Thus it's not surprising that all languages have evolved to about the same speed. None is "better". They all convey information at the same rate. That's why there is no pressure to speak just "the best one".
Like you, to my ear, American English seems to be spoken at different rates regionally. I don't know how to think about that...
I tried learning Danish. It's not like French where you don't speak the ends of many words. There, you just say only the most important syllables in the sentence, usually "deh" or "leh" (which are pronounced the same). Respect the Danes! Their language is impenetrable!
That's not how the evolution works actually. How it really works is: “If it's better at spreading itself then it will take over”, but it says nothing about the intrinsic quality of the trait. And for memes (literally speaking, as described in the last Chapter of Dawkins' Selfish Gene) it means being cool enough for people to copy, no matter if it's actually more efficient at conveying information or anything.
We can think of a language like a digital modulation, with the set of sounds being a symbol constellation, and the syllable time, as the baud rate. When you do such numbers, most (all?) languages fall in a fairly narrow window (something like 30 - 50 bits of actual information per second at average speaking speed).
If a language has fewer possible sounds, the syllables come more quickly. This is an innate tradeoff with a communication channel in information theory.
But the analogy is only partial because, unlike most designed protocols, the symbol distribution is not a normal or random distribution. And human language has, in information theory terms, internal redundancy and compression (pronouns do a table lookup) as well as error correction codes and checksums (most combinations are illegal).
This makes a analogy beteeen spoken language and a modem less than straightforward, though they are governed by the same underlying laws.