The streaming world has grown complex. In simpler times, there was Netflix and Hulu, along with a handful of niche services to choose from. But now there are more than 200 streaming services crowding the marketplace, competing for viewers every day. The good news is that only about six or seven of those are dominant, but that doesn’t make the space any less contentious.  Though the field is turbulent, Susan Ennis, a former Executive V.P. at HBO, brings with her the expertise and insight that can help us put the streaming wars in perspective.