You've got the definition of Magical Negro wrong, there is nothing in the definition about:

perfect people [...] they can do no wrong

Here's the definition from the wiki you linked:

The Magical Negro is typically but not always "in some way outwardly or inwardly disabled, either by discrimination, disability or social constraint," often a janitor or prisoner. He has no past; he simply appears one day to help the white protagonist. He usually has some sort of magical power, "rather vaguely defined but not the sort of thing one typically encounters." He is patient and wise, often dispensing various words of wisdom, and is "closer to the earth."

Notice the complete lack of being "perfect people" or doing "no wrong."

The link to Sambo, and Nobel Savage is key to understanding the nature of the term. If you told Spike Lee he had a Sambo, a Noble Savage, or a Magical Negro in one of his movies, you would be accusing him of using racist imagery.