This video was linked the other day, and since I enjoy foreign languages as a bit of a hobby I listened to it while I did some laundry, and it was fascinating. The man describes how various African languages were strictly oral for so long that their concepts of higher-level abstract things never developed as a result. They didn't know why you would have a dictionary, for instance. There was a distinct lack of precision in their languages and it showed, and it also shaped their culture permanently.

To answer your question, they are literally not as functional and useful as English is, and there is no argument about it. There isn't a single thing you can say in any African language that you cannot say in English, especially when it comes to abstract concepts like promises, honor, integrity, time, space, and personal relations.