For most U.S. PhD program in economics or business, we can see approximately half of PhD candidates are Chinese students. That's a fact but not a indicator that those programs have any problem. We have to admit that the U.S. PhD programs are most rigorous among the world. And I have to say that economics PhD is a bit of oversupply but business PhD is still scarce.
And, income of new business PhD graduates is really good, which may reach $100,000 a year!