Follow-up after an afternoon of reading: I dug into the source of the data you presented here in references [1] and [2], which is mainly from James Fearon "Ethnic and Cultural Diversity by Country" (2003). In this he actually explicitly cautions against making the kind of analysis and correlation that you posit here:

> First, it cannot be assumed, without argument, that ethnic distinctions are wholly exogenous to other political, economic, and social variables of interest. For example, poor economic performance could exacerbate distributional struggles, causing people to see and act along lines of ethnic division that were formerly considered unimportant. By contrast, robust economic growth might lead to the downplaying of ethnic divisions and a greater emphasis on national identity. If Botswana seems more ethnically homogeneous than Somalia does at this point, it may be that this is in part a result rather than a cause of economic growth.

The paper also goes into great detail on the problems inherent in trying to categorize ethnic groups; these two factors combined are why I object to your methodology here and I would recommend that you read the paper for yourself. In other words, any conclusions drawn or inferences made based on this data without controlling for innumerable complicating factors is likely to be a case of garbage in, garbage out.

Of course, ethnic diversity is just one of many forms of diversity, which further removes this data from your argument.