Note the qualifier. “Relatively reasonable”. In contradistinction to the Zulu, who are regimented and have a hive mind. Mandella, communist that he was, still saw the necessity of creating a black middle class to facilitate the transition from Apartheid to an integrated polity. Unfortunately, he died, and afterwards so did his efforts.
The Boers did not own slaves after the Great Trek, because in the Grahamstown Manifesto they declared that they would no longer own them, but would make such laws as were necessary between masters and servants. Arguably, the colored and black servants that they kept on the veldt were more like serfs than actual slaves. Many of them perished in the concentration camps that Lord Kitchener set up, along with the “memsahibs and “little baas” to whom they were connected.
Yes, I do know all about the Brits invention of CONCENTRATION CAMPS, which were as brutal as one can imagine.
OTOH, in more modern times, blacks who worked for whites were NOT normally ( I don't know about EVERYBODY, but DO KNOW about many! ) treated quite well.