Big Data is not infalliable. The flaw in Big Data is when it asks the wrong questions, or fails to ask questions the correct way.
I think you are totally wrong in saying vanilla wow would not succeed today. If you want to say people would dislike balance issues in vanilla wow, or the raid design, that might be true. However, I think the fact that vanilla wow is tremendously SOCIAL with vibrant in-game communities would totally overwhelm those negatives and a vanilla wow server released today would grow to 20 million + subs. The reason is the PRIMARY appeal is the social factor.