You are correct and your correctness is painful.
Mandela is not the only advocate of freedom to smack into power — Gandhi comes to mind, or the fracture on the shoals of egos after the French and Russian revolutions, or even the close call with disaster the young United States had in 1800.

It’s easier to seek power than to wield it. Still, I must admit that the South African constitution is a work if art with a bill of rights that puts ours to shame. And South Africa came with a Bar toughened in the fight with the apartheid laws. These are advantages that many of the nation-states that grew up within illogical colonial boundaries lacked.

Breaking rocks on Robben Island all those years, Mandela had the long standing tactical disagreements with the Pan-Africanist Congress on one side and the Nationalist government in power on the other urging him to just renounce violence and expel Communists from the ANC and his release could be worked out. Had he caved to either side, South Africa would be much worse off now.

There was never any question that Mandela would head the first post-apartheid government but also that he would be elderly when he took over and the knives would be out over subsequent leadership. As best I can tell from a distance, he put country before party and left institutions that could navigate the challenges with the right leadership.

Compare the economic and political disasters of Zimbabwe and the former Portuguese colonies, all of which were struggling for freedom at the same time. Yes, you are right, and the problems go much deeper than Zuma’s idiocy. But the tools to repair the damage are still available.