Since New Zealand passed MMP 30 years ago, every Prime Minister has come from the same two parties that have dominated NZ politics since 1935.

Two party systems also are built on coalitions. It isn't as if "Democrat" or "Labor" is a unified ideology.

I'm all for MMP but I don't think it will fix any problems in American politics.

Just introducing MMP would add another veto point in an American political system that already struggles to actually accomplish anything.