In the rest of the world, private homes installing solar panels and batteries is seen as a good thing. Doesn't this at least give South Africa a head start in something, even if energy grid instability continues to be a problem?
You're effectively describing the "Parable of the broken window". Solar panels and the systems to run them now represent a significant outlay by businesses and some private individuals. Other countries don't have these expenses so the net effect is that South Africa becomes relatively less competitive and less attractive for investment.
Only a small percentage of the population are in a position to afford to install private solar. So while its great for some it doesn't help solve the issue for the majority.
The thing is, the small percentage of people who can afford the panels already subsidized a large part of the energy supply to the population. In the south african townships, illegal connections to the grid are very common and a substantial part of the population lives in such areas.
3.5GW is almost 4 levels worth of loadshedding...ok sure it won't have 100% efficiency but South Africa is one of the best countries in the world for solar.
If solar keeps getting installed at this rate, loadshedding will be just about completely averted within 2 years, for the entire population - whether you have solar or not. Poor people are benefitting from solar already from lower loadshedding levels, and by having more reliable power at work (since many businesses are now running on solar out of necessity...and generators of course)
SA still has a mostly functioning grid, just an ancient fleet of coal power stations and badly built new ones that don't give the power needed.
So while many homeowners wouldn't have installed solar if they weren't forced to, they (myself included) are also discovering that unlimited free power when the sun shines is awesome, and with a decent Lithium PO4 battery it's not hard to be fully off grid for much of the year. "Green loan" schemes from many banks are covering installation costs and it's easy to save more than half on you electricity bill since most of SA is really sunny.
+ the environment is a big winner...the more power plants worth of power that can be installed in solar & wind, the more old coal plants can be shut down forever.