You would have to compare the GDP to some measure that better maps to real world value. And the choice of measure to use would be controversial. HDI? GNH? HPI? GNW?

I agree that GNP is a terrible measure of real world value (a lot of things increase GNP that decrease human well-being on a global or long-term scale). But if you want to falsify it, you need some other measure. Is the other measure falsifiable?