He would be the greatest economic genius of all time if he could pick where t* should be in what conditions and variables are going on such as wars or disasters or boom times.
True enough.
But just because a tool cannot provide 100% accuracy does not render the tool invalid.
I may make the prediction that certain atmospheric conditions may produce a given effect.
Just because those guidelines are not accurate to several decimal points does not mean those guidelines are not a useful predictor of weather.