Earlier quoted context omitted.
> Parliamentary systems are generally considered more stable Hm... Germany's system changed at least 3 times in the 20th century. France is on its Fifth Republic. Italy is a shitshow. To me it seems that the oldest democracies (UK, US) are the most stable (even today!) and they're majority systems (first-past-the-post).
To actually do comparative politics, you need to regress over regimes not just call out counter examples. This is a quantitative problem, not a logic problem.
The worst case for representative democracy is literally Hitler. The second worst (you could argue that Hitler was a unique set of circumstances) is the dysfunctional German, Italian, or French states.
The best case is probably Switzerland (party proportions barely change, I assume because the power of parliament is diminished because of elements of direct democracy that Swiss practice).
What's the worst case for first-past-the-post democracy?