I agree that the top universities in China are full of good test-takers and I was one of them. However, Chinese education systems totally focus on exams and every college student is a good test taker, trained to be from elementary school, because otherwise, you won't suvive the system. There is only one standard. So it is almost impossible to define 一流学生.

The education system in the US is different. There are too many opportunities in this land. Many talented students don't care for exams. I was on the graduate committee. I can tell you that, for Americans, recommendation letters are more important than GPA (in most cases) when they apply for graduate schools. Medical school admission is more competitive than graduate school in general. That is the reason why the pre-meds always ask professors for more points. I also suspected a pre-med cheating in the exam once, not enough proof though.

The total number of students in Sciences and Engineers are declining in US. No doubt about that. But if you look at the profiles of the American graduate students in top univerisities, I think you would agree that they are really 一流学生.