If you use these methods and you get the same result for Barbados, with an economy the size of a small county in an obscure US state, as you get for the entire US, shouldn’t you be sceptical? The truth is that economies are so diverse in so many ways that the notion of universal theory is problematic.
First, it is very difficult to accurately estimate the output gap, which is the degree of excess supply in macroeconomic terms. Second, it is likely that the potential growth rate has recently declined substantially as a result of stagnant investment over the past ten years.