>Their intentions were mostly based on philosophical guess work, as they didn't have a whole lot of empirical data or existing republics/democracies to base their new government on.

They had plenty of examples to base their design on; democracy had been invented more than a thousand years before the US was formed. Like the vast majority of social institutions though, it was in the end based on fallible guesswork -- people like Thomas Jefferson were explicitly aware of this.

What they could not have planned for was the industrial revolution, corporate proliferation/globalization, the information revolution of today, and the scale of it all.