Well then, how does the EU (whose central authority is extremely limited in scope compared to the US Federal Government, and whose member states are still meaningfully sovereign separate countries) manage to thrive so well?
Why couldn't a similar system work well in the US?
Have you not heard Europeans talk about the EU? Pretty much everyone agrees that it's slow, cumbersome, and doesn't address a lot of problems quickly enough. It's also significantly more complex[0] by further dividing the executive position, compared to the American system, and it's only got 28 states.
Why couldn't a similar system work well in the US?