I won't disagree that he is competent, but at the YC talk in New York, his public speaking was filled with filler sounds where it seemed he was nervous to talk in front of a large group of people (even if that was not the case).
Not sure if you've already seen this, but he wrote about his thoughts on speaking and writing [1]. He does admit that he isn't the best public speaker but puts more value in content rather than presentation in these situations.