I think you miss understand me. Whitaker was a very effective defensive fighter, in that he was hard to hit and hard to figure out, but he was far from a classical defensive fighter. He had a habit of squatting very low, well below his opponent's waist, which, technically, is illegal. He also had a tendency to grab around their legs and lift them (against Nelson, for example). This, also, is technically illegal. He got away with it and more power to him, but the best way I can think of to describe it is "herky-jerky nonsense."
Whitaker did not have the best chin; early in his career, especially, it was a source of much concern. Later, Hurtado put him down a couple times. Perhaps this contributed to his unorthodox way of avoiding punches. My belief is that Norris would knock him out, and Pernell Whitaker wasn't the type of fighter that you beat up on. I think that, at some point, Norris would have hit him and stopped him. That moment may have come in the first round; it may not have come until late, but it would've come. I think it would've been in the 6-8 round.
Incidentally, Freddie Pendleton hit Whitaker and made him shake a few times in their fight and a one-armed Buddy McGirt fed him right hands like peanuts. Norris stops him.