The social cohesion of Switzerland is mainly within the linguistic communities. Many Francophone Swiss hardly speak a word of German (just as their Belgian counterparts don't speak Dutch). And a large proportion of Switzerland's "diverse" immigrants are in fact from just across the country's borders (particularly Germans). "Diversity" is not what explains Switzerland's wealth.

Absolutely agree, and of course I would never argue that "diversity" explains Switzerland's wealth. It occupied a pretty unique and interesting place during the Reformation, and maybe there is something there. But the idea that either diversity or homogeneity can explain economic performance is obviously not bourne out by any serious examples. I was thinking about Belgium (and also thinking about Harry Lime) whilst typing away--it seems a bit of a counterexample to Switzerland where the same linguistic and cultural diversity within a country can lead to very different outcomes and senses. Nobody would ever write "Il n'y a pas de Suisse" as Destrée wrote "Il n'y a pas de Belges"--long history vs short history and as always the Reformation upheavals explain it perhaps