They speak different languages, French and German, they have different churches, they were killing each other up until 1848. Very important. They were killing each other until 1848, Sonderbund Wars. The system is the reason they stopped killing each other. They are not heading for civil war like all the other "democracies".
There's also Islam in the picture (in more or less the same percentage as other Western Europe countries, 7%) and they're also integrated, you don't see the problems you see on other Western Europe countries like the UK, France, for example. Also not trivial at all in my view.
The system works. I think the scale is irrelevant. It's more than clear for me the more I study it. The system works and we gotta learn with what works.