Dr. Watson is an active device. Dr. Watson actually performs protocol interactions with other devices on the network. Packet monitors are primarily passive devices which merely show you what packets happen to pass on the network. It is not so much a matter of being better or worse. Rather, it is a difference.
Passive monitors have their place.
However, active devices can actually exercise the network, interact with other devices, and, in general, do a much better job of verifying that your network is acting properly and that devices are responsive. A passive device, such as a packet monitor is like a person who watches a game of sports on television. Dr. Watson, on the other hand, is like the player on the field. Dr. Watson can. Experienced users equipped with both Dr. Watson and a packet monitor usually find that Dr. Watson is the first tool they use when dealing with a network problem.