> The exact opposite is true. The only consistently working, stable democracies do not have a single leader of the executive branch, e.g. Switzerland.

That's correlation, not causation. Switzerland made enormous amounts of money from its banking secrecy system over many decades until the US pressured it to end it. And the trends are not looking good for Switzerland based on data. We'll see how stable it remains as the cost of living keeps rising, real wages decline, and unemployment goes up.

If you provide wealth and a good lifestyle to your citizens, then almost any system will be stable.