Don’t most of them return to their home countries? Seems like freeing up those spots for American students that will stay would be a boon for American science.
They often do have more money. And rampant cheating. But regardless, Chinese students can attend any university in China or the US, while an American cannot realistically attend school in China. Obviously that means China is going to have a brighter educational future, as they use our system to advance their own.
It makes a very big difference in getting there.
If they are replaced by less capable students then the work being done will be of a lower quality.