It is not that McKinsey could be blamed for Eskom's general inefficiencies but rather that it shares responsibility in the lack of a managerial and efficiency turnaround at state companies like Eskom.
The general rhetoric is to blame the government (perhaps correctly), but the present article I think does not attempt to singly shoulder responsibility on McKinsey. It shows how government inefficiency may lead to a general free-for-all or at least a atmosphere of being exempt from justice in the private sector as well.
My summary on the matter would be that many South Africans have the desire to build towards a more economically competent country and that complications in bureaucracy and malevolent actors complicate this. This is a country where anyone rather easily can weaponise different kinds of racism or partiality that degenerates into a debate about whom we should blame. In preventing this particular counter productive and frequent exercise perhaps it is useful to remain as objective as one may be in identifying responsible parties, letting them be held accountable in the corresponding legal framework, and from there focusing on actual problems such as the state of disrepair of Eskom run power stations. It may well be that action by private companies would catalyse the process towards an efficient and economically sound South Africa. However, what this articles shows is how an internationally respected private firm fell into the same traps that local politicians do.