The book by Scott E. Page "Diversity and Complexity" is a useful complement of the book written before by the same autor, "The Difference," offering definitions and taxonomies of diverse and complex systems.
In that previous book, Page argued that diverse preferences, although presenting social choice challenges, also offer the opportunity for diverse perspectives that help to solve problems with uncertain solutions. Diverse communities or groups do not succeed automatically, as cycling is not something that one learns without some training. But once you learn, cycling goes much faster than running, which is much easier.
Complexity comes from systems that result from the interaction of diverse adaptive units from which patterns emerge that are difficult to predict in advance. A calculus exam is difficult, but not complex, because the parts do not interact.
The more recent book explains that the role of diversity is to provide insurance, competition, redundancy, and innovation. Although the book has mostly a positive tone, it also reflects a preference for diversity. This preference then must be implemented under the positive constraints set out in the book. There are many examples of this, and that is one of the good reasons to have institutional diversity. A preference for diversity makes many of us prefer big cities rather than small villages, although the countryside is also an example of natural diversity. The author is very aware of the constraints: diversity is no panacea and not every kind of diversity works. If we put lots of randomly different things together they will not create a coherent system from the beginning. In nature, diverse ecosystems work precisley because they have been evolving for centuries. The book has many interesting insights beyond the relationship between complexity and diversity, like the distinctions between data, information, knowledge, and wisdom (in increasing order of structure).
In biology and non-human nature, change comes from evolution. In human societies, it comes both from evolution and from creative intelligence. However, intelligence has plusses and minuses, the latter especially coming from confirmation and other biases.