Some thoughts.
I suspect that when a government is unable to scale its ability to govern, the statistics become dopey.
This doesn't imply a conspiracy necessarily. It could be for instance that if people stop reporting crime, that either the crimes are not occurring or that people's faith in the government to provide effective policing is undermined.
This makes a government's statistic's office an unreliable narrator even if every person is not corrupted and competant at their job.
Semi-related: I feel a faint thrill of unease at this reasoning because of the broader notion - that any society going into reverse wouldn't be sensible to what was happening: things would just gradually get weirder. Nobody would know why. A society suffering from Alzheimer's disease. It would just get worse with the ability of society to possess executive function dropping off at a similar rate to the ability to physically function. Eventually people would be looking upon the ruin wondering what the fuck happened.
Second thought.
Although no expert on SA's economic infrastructure I do know one thing which is at odds with your portrayal. Escom is the almost exclusive provider of electric power, still owned by the SA state IIRC. It has not added any electrical generation capacity to the grid since Apartheid. Their facilities are also badly run down.
How can you claim then, that more South Africans have access to electricity? Were white people hoarding all the electricity and now it is more evenly distributed? It seems more likely that more people would have obtained access in name only.
> quality of life has gotten materially better for the vast majority of people (coming off a low base), but worse, or stagnated for those of us SA'ns well-off enough to frequent HN.
I concede it is possible I have obtained a biased version of reality from those South Africans capable of net access.
I'd suspect though that most right wing South Africans would have left 20 years ago, so the people left in SA must be the more Liberal and Left of center portion of the population, or those unable to leave. If this is true, and we believe that political character is mostly hereditary (I do), then the bias may lie in the opposite direction.
That most media sources bias would be in that same direction nearly goes without saying. Western media trumpeted a great victory after Apartheid after all.
Final thought:
For what criteria would you concede being mistaken? Mine is simple: if South Africa experiences significant increases in real wages and life expectancy goes up, then it is successful.
I put to you that since AIDs should be fatal to those without access to expensive drugs, and infant mortality likely is dropping as you said you should expect an uptick in life expectancy over the next few decades.
Were that not to occur, then something is wrong.
I know some people believe the tentacles of the former regime have gotten stronger over time but this seems conspiratorial to me and I've never heard a fleshed out explanation for why that ought to be so.