By now the world knows that Sir Martin Sorrell has left WPP, the business he founded 33 years ago. I'm old enough to remember the ad world before WPP. Sorrell transformed his industry, and there aren't many in any field who can legitimately claim to have done that. Forests of newsprint and millions of pixels have been devoted to analyzing his legacy. Was he a good or a bad influence? Will he be missed? Are we all better off without him?