As I've heard it, diversity being successful is based around the idea that a homogenous people will use traditional methods to solve a problem and they will solve the problem faster using that traditional method since they are all on the same page.

With diversity, they take longer to solve the problem, but supposedly their solution to the problem will be new method that is "ground breaking". I've yet to see evidence for this.

What I have seen is evidence that suggests that diversity causes social disunion and distrust amongst neighbors and in society.