I don’t think the problem is that the government “wasn’t the best ever,” I think it’s that it hasn’t changed. And the US hasn’t done a lot to enforce some of the groundwork beliefs of the framers.
I still think the idea and balance of power of the US government is one of the best—but it was created to change with the times and address practical flaws (amendments) and hasn’t.
The problem is that they're still largely perceived as being the best ever. The American founding fathers are pretty much deified, and it's still expected that important policy decisions will be made based on what these centuries-dead aristocrats thought rather than based on what's needed in the here and now. Other countries don't do this. I've never in my life heard a politician try to attack or defend a position based on what John A. Macdonald would have thought of it, but in the USA that sort of thing happens all the time.
Yeah, but that's a structural flaw inherit in the initial design. We were doomed to quickly end up in a two party system, despite the fact that they all thought they were better than parties. The federal government pretty much immediately became a two party affair, that that inherently stagnates change and limits the actual will of the people from being enacted in government.
Many liberal countries have these alternative voting systems, and it means nothing. Australia and Japan for example use alternate voting systems, and yet are still far-right countries who are killing indigenous movements and have extremely unpopular governments.
The root problem is that in liberal countries, capitalists stand above the political system, and control it for their own purposes. No people's democracy can emerge from within it, regardless of any system of "checks and balances" or voting systems.