If you don’t know, why are you so confident your idea is right? “Diversity” posits that, for example, an all Chinese team would be improved by adding Mexican people. Feel free to substitute any other groups, if you like. This is an idea you apparently subscribe to, so why can’t you provide a concrete example, and instead speak only in abstractions?

The fundamental problem with your reasoning is that you’re taking on faith the notion that differences are good ones. There is no reason to assume that. If differences between people can be good ones, they can just as easily be bad ones.

So you just take for granted that cultural exchange is a net negative? Why do you think people won’t learn anything useful from another culture?

Since you insist, I can provide a personal example. My former boss is from Colombia. I’m from the US. He insisted I take more time than I would have chosen when my child was born. He said this was based on his cultural upbringing in which family takes precedence over work. I appreciated that and I feel that it prevented my burnout.

Here’s a well known case: Kaizen in manufacturing, which was originated in Japan based on a mix of American and Japanese ideas then reimported to America.

I base my more general and abstract belief that cultural exchange is good on many examples throughout human history. Cultures that don’t admit new ideas generally haven’t fared well in the long term.

If you optimize for "different kinds of people" you cannot at the same time optimize for academic performance or IQ. You have to choose less capable people just to get more diversity. There is plenty of evidence that intelligence causes success on all kinds of measures, but I have never seen a study about racial/ethnic diversity causing success.