While I doubt that's the case for either (them being sustainable), you raise an important point.
What we call "success" (economic, and so on), might be in fact a liability (environmental, societal and democratic debt), and countries doing worse than US, Germany, China, Japan, and so on, might be much better in actual sustainability and future-proofness.
The problem is we talk about "progress" without ever mentioning progress towards what. More GDP, more consumer gizmos, more productivity, etc -- but rarely we talk about preferred ways of life, maximizing happiness, inequality, democracy, and so on.
Both India and South Africa were British colonies who had some elements of British politics & liberty passed onto them. The freedom of these peoples, if they maintain it, will be down to their history.
Other nations, particularly in Africa, are looking keenly on at China's economic miracle, and realising for the first time in history that liberalism is not a requirement for a thriving market economy. For decades, if not centuries, this has been the established rule. What's so dangerous about China apparently breaking the rule is that every leader, autocrat and downright despot with a population hungry for a better life will now realise that there is a path where they can give their people a better life but they can keep their own power. Before, it was clear that liberty, at least to some extent, went along with prosperity. If and when when African nations get their feet out of the mud it will shake the foundations of the global order. I desperately want to see their power and authority granted and restrained by free and equal peoples. If they follow in China's footsteps that certainly won't be the case.
Do it wrong, however, and you can end up like Zimbabwe.
The track record of the South African state in the past decade has been depressive. After they booted Zuma there is probably a chance to do better, but it's not obvious everything will go well from now on.
One thing to keep in consideration about the South African situation is that land reform in South Africa is not new; it's written into the constitution. What's new is that South Africa is dropping the requirement to recompense the owners. This could be a problem, not just for the white South Africans but for black South Africans as well as it could drive the middle and upper class out of the country.
https://en.m.wikipedia.org/wiki/Land_reforms_by_country
The dearest to me, however, is what was done in my native country, Finland, in the 17th and at the turn of 19th and 20th centuries which created the basis for our current national wealth.
To simplify a bit too much: a succesfull land reform looks like splitting the ownership of land which produces agricultural output or timber from few large owners to many dedicated ones. This distributes the revenue from capital among the population using a " market healthy" method. Rather than spread the revenue from the capital, spread the capital itself. This is a solid foundatuon for creating a wealthy middle class - which has been identified as one of the key parts of a healthy modern economy.
Zimbabwe just took the land from it current owners - which were already spread among a fairly large population - to complete people who could not tend it as well, and not utilize the capital as effectively.
England is an easy place to start because the common language leads to an extensive Wikipedia article, but you'd find similar ones for any European country in their own language, especially since most experienced the upheaval of revolutions, conquests or occupations. The US had common trends but different details for each state.
[1] https://en.wikipedia.org/wiki/History_of_English_land_law
[2] Failure to redraw maps had meant that sometimes one landowner was the constituency behind a seat in the commons https://en.wikipedia.org/wiki/Reform_Act_1832
For example, abolishing serfdom made your land less valuable if there were no longer people that belonged to it. Or, confiscating monasteries and abbeys, then gifting them to favored nobles is a form of land reform. Similarly creating the conditions that the large manors dissolved later is another form of land reform.
In California, you can look at the title histories that trace back to large ranchos from the Mexican period and before, and look at how ownership changed hands. Most owners were legally entitled to retain ownership, but any number of tricks were used to get them to lose their claims.
The same goes for changes in ownership of water rights, mineral rights, air rights, or new limitations on what types of commercial activity are permitted.
The measures can be beneficial or not, but it seems extremely common for changes in public policy to alter property rights.
Kerala.
Not sure this would work for ZA though. Namibia is only 2M people, it's not the same scale.
How convenient, as the end of apartheid was less than a generation ago (1994). What's done is done, right?
Everyone is worried land appropriation in South Africa is going to kill agricultural productivity like it did in Zimbabwe, where the farms were seized and given to individuals that had no business being farmers.
These countries still have a version of capitalism that is not as aggressive as the Anglo-Saxon model, and a democracy that is far more permissive than the East Asian (barring Japan) model.
Indian or South African growth may not be glamorous, but it might be sustainable. (And the population growth in both places is far less alarming than generally thought.)