My understanding is Mandela was a respected leader who was willing to play ball and facilitate a peaceful transition where the white leadership got to keep all their property. That's why there's still massive economic inequality in SA today. Not to say Mandela wasn't admirable or that he didn't suffer, but it was a conscious choice to avoid outright military conflict at the cost of preserving an implicit racial hierarchy.
To me, the peaceful transition is the achievement. It is the amazing part of it.
First, there was significant pressure on de Klerk from Western governments. Thatcher told him to release Mandela, for example. The reason she did not support sanctions is because they would likely harm South Africans for no reason...this was justified by later events. As pressure on de Klerk would have made it a lot harder to negotiate with Mandela freely.
Two, de Klerk became leader and his first action was to try to form a path to reconciliation. Mandela played his part by abandoning terrorism (I am not sure why this is disputed...this is what Mandela said about himself). de Klerk's position was, however, not particularly easy because whilst everyone acknowledged that the system had to change, it wasn't clear how to get to that point.
Three, the article implies all white South Africans were racist...this is not true. This assumption is not why apartheid happened either. de Klerk was not Botha. The US experience dominates the world, the assumption that everyone in the NP was racist is not accurate...let alone saying everyone of a certain race must have been racist.
Four, there has been massive upheaval. The economy of South Africa has collapsed, and the ANC did seize property under the auspices of BEE. Large companies were told they had to hand shares to ANC members or they would be shut down, these companies then took out loans to buy back their shares. The current President was a friend of Mandela, union leader, he was then gifted hundreds of millions in shares...that is how he became wealthy (and, if you can believe it, he is the "anti-corruption" guy).
Five, the reason there wasn't bloodshed because there was a transitional period. This was agreed by both parties, this is why Mandela wins plaudits for recognizing that NP had legitimate concerns that had to be taken into account to move forward. But...this still hasn't stopped the country collapsing.
Six, the argument that there must still be racism because of economic inequality is a uniquely US take. The ANC expropriated wealth en masse, the majority went to party insiders, and there has been almost no interest in serious economic policy-making because...the country is majority black, and the ANC are the black party. The reason people are poor is because there is no education and so they have no skills, crime is also out of control...this doesn't have anything to do with someone else not being poor (and btw, almost everyone in South Africa is now poor, the currency has collapsed, everything has collapsed, there is so much corruption that electricity cuts frequently...yes, those white people again though...this is why Malema is popular).
Seven, it was reasonable for de Klerk to be wary. What happened to Rhodesia? Everyone has this idea that everything would be fine, just trust Mandela...okay, there is a country next door where you saw whites being slaughtered en masse when Zanu-PF took power. The country has still been ruined, but that didn't happen at least.