The thing is, the UK doesn’t check those boxes either . It is also a first past the post system, almost uniquely so along side the US among modern "democracies ". It’s no coincidence in my view that the two countries have gone down a similar path.
That said, of course you are right that extremism is a problem even in more mature voting systems. But two party systems and the politics of “tear down everything the previous government has built” is unique to first past the post.
There’s a reason people in the UK campaigned for years for a change to the voting system, finally got a referendum and got scuppered by the government presenting an obscure and unwieldy form of representation as the only alternative in the referendum and by campaigns like this. And no, this isn’t parody, this was an actual ad campaign at the time.
