That is an interesting statement…
Below is the total return performance of the Swiss market over the last 20 years. 22% over 20 years makes 0.9% per year on average. I am not sure it even beats inflation.
MSCI World on the other hand went from 1141 to 2044 on the same period, which makes 83%. Not incredible, but already better (3% per year) (I could not find on this graph if it was total return (including dividends) or not).
Maybe Switzerland will continue to be a stable country, as it always has.
Or maybe the Swiss National Bank will have printed so many franks that the whole Swiss economy will tumble.
Or Maybe Switzerland will do just fine, but US will collapse with all their debt.
Maybe Japan will wake up from two decades of non-returns and become a competitive stock market again.
Or maybe not.
My point is, if you start indexing, you do not want to guess what will happen to a given country over the next decades. So your best hedge is to buy companies making earnings everywhere in the world, so that what happens in one country has less effect on what happens to others. This is what a world index does. This is what the S&P500 or VTI does as well in a certain measure, since all those companies make money all over the world (even if they are incorporated or listed in the US).
All this global flow of earnings is the best hedge against any currency risk.
Don’t forget that, over the long term, the valuation of an index is how much value and earnings its companies are creating. It does not matter in which currency it is expressed.