I don't think you have to be a good director, or good anything really, to make a very interesting movie, IF you bring an entire freaking ship into the jungle mountains and such.
You can suck a lot, and still the movie would be exceptional
He was also cheating with Klaus Kinski. Just have him in front of the camera, no script.. as long as he doesn't actually kill anyone or get killed, the movie is good.
But Herzog was not cheating. He is also a good director, on top of all of that