Resource wealth doesn't lead to general prosperity. Look at Hong Kong. Then look at Saudi Arabia. Then look at Russia. Or for that matter, all the countries in West Africa, which are horrifyingly poor, yet awash in valuable minerals.
What leads to prosperity (see Thos. Sowell on this) is the rule of law and a physical infrastructure that allows for trade inside and outside the country.
Compared to the rest of Africa, which is much more tribal and corrupt, South Africa excelled in both law and infrastructure. (Even bad or imperfect law is better than none, if it can be counted on.) It therefore developed a real economy, and compared to the rest of Africa, a real political system.
The kind of organized looting of a country that went wild in Zimbabwe-Rhodesia and seems still to be sinking South Africa always leads to financial ruin, because it destroys confidence in the law, and reduces entrepreneurs' willingness to take the risks that produce general prosperity.
This is a classic fascist argument. Would you say that Germany circa 1939 was a better place than Botswana 45 years later?