That is...an extremely narrow study to use to make that broad an assertion. GPA of two classes from 2010 at a single business school in China, their starting salary, and then their salary in 2018?
Why is it narrow? N is a few hundred at a well ranked and good amount of rigor university, and is aimed at the graduating class and then their earnings as they rose through to probably mid career positions past entry level.
I haven't read the entire study mostly because I don't care, but I think you're wrong in your statements.
GPA is well correlated to earning potential, as well as earnings in reality.
That is...an extremely narrow study to use to make that broad an assertion. GPA of two classes from 2010 at a single business school in China, their starting salary, and then their salary in 2018?