Fundamental economic theories are unrooted by elementary math.
GDP is just as relevant as an indicator of economic gameplay as the score in soccer is an indicator of the quality of soccer gameplay. Indeed, quite irrelevant. And its dependence also suggests two soccer games ending in the same score must have been derived from identical gameplay. Yeah, right.
A score is a derivative, a consequence of a situation, not the cause. Meaning, one cannot, from such a derivative, revert to an irrefutable cause. As in 2+2=4, yet 4 is not always 2+2. Now, consider the complexity of more compounding equations making up the definition of GDP, which, btw, varies per country.
Comparing GDP suggests exclusive symmetry between the two equations, a flawed supposition adopted by every economist I know, with its make-believe eagerly sold to politicians, asset managers, and investors.