We haven't even set criteria.

What makes a good system of government?

Number of people ruled? Years of stability? Average happiness? Number of countries colonized? GDP? Size of income disparity? Number of pyramids built? It really doesn't take much until you could argue that Monarchy has a WAAAAAAAAAAAAY better track record.

Every form of governance eventually emerged to deal, best as we could, with the constraints and tools of the time. Those that figured these things out the best and cooperated within their in-group better got to live the life, and those organizations that failed this test or held onto previous survivorship bias a little too long, well we try to not dwell on their fates.

The key ingredient is that circumstances change surprisingly often. People live in different places, do different jobs, different life expectancy, access to education and vastly different communication networks. For as little as I could without bias say that I know what is the best, I can say that it's either going to be a significant departure from the past or that America will find itself relegated within a generation or two.

This is the simple truth: The world is not the same. Ideals that however briefly seemed reasonable, even if they never held up quite the way we'd like to believe, don't anymore. And that every empire of the past believed itself eternal too.

tl;dr: Ya gotta change to keep up with the world. The dream of the 50s isn't cutting it.