Canada

That is my favourite kind of question! Unfortunately, social sciences are pretty hard to demonstrate causation. (Any research would involve so many subjective decisions, e.g., Turkey is nominally a PR country but I imagine İmamoğlu and others would uhhh, have strong disagreements with that. Do you count poorer countries with a complicated recent history? If we restrict too much the sample size becomes negligible etc.)

But, after having doorknocked and bugged friends to do so as well for proportional representation in 2015, I've watched what's happened across the world since and it's spooked the shit out of me. In part, what I've seen are the causal mechanisms, which I think are twofold:

1. FPTP disincentives fringe/extreme parties. Think back to the thankfully short lived PPC here. That's not to say they can't take hold, look at Reform UK or the Republicans. But, in both cases, it took the collapse or infiltration of an existing mainstream party, which thankfully, is pretty rare. As much as I dislike and disagree with Polievre, few reasonably informed Canadians would put him or the Conservatives in the same bucket as the far Right parties in Europe/America.

2. In recent, more polarized years, it's been harder for parties to compromise to pass significant legislation, which has resulted in surprising stagnation and papering over problems. As a joky but illustrative example, in Germany, the trains no longer run on time! (Seriously, if you've been to Germany 20 years ago, you'll know what a bizarre thing that is to say. It'd be like basketball replacing hockey here.) But that inability to pass bold, significant legislation means problems don't get addressed and people don't see much significant change in their lives.

Our system has a lot of faults. But in my eyes, the biggest strength is that a government with a majority can really do things as there are fewer checks and balances. Think back to how effective and targeted CERB was, proportionally, we spent a fraction of what the US did but it helped people who really needed it and quite well. Despite being interrupted by a pandemic and then fighting off challenges to his leadership, Trudeau still started us on a path to subsidized childcare (absolute game changer if we can get that over the finish line) dental and pharmacare. BUT, for all that strength, it also means we are much more susceptible to disastrous outcomes with a bad government.