I can't imagine a person who thinks the US is somehow "perfect". I view this as a nonproblem, anyone with such a view is irrelevant.
I don't get wound up about "world's greatest country". If one attaches differing metrics, you get different outputs. Maybe the world's greatest is the one with the happiest citizens measured by polling. Maybe it's the one with the largest GDP (per capita perhaps). It's like greatest BBQ joints, or wines. Make a list, throw it away, life goes on.
As for the Constitution, I think many of us here would like to amend it one way or the other, term limits often comes up.