Henry, the pump is far better than the sensor for getting good blood sugar control, and having lower A1c's. Using carb counting, knowing your insulin sensitivity levels and testing frequently are all important in getting improved control. The book "Pumping Insulin" by John Walsh is a good guide to follow in learning to use a pump properly.
The CGMS (with sensor) enables you to see "trends" that tell you when a high or low is approaching. Knowing ahead of time enables you to take an appropriate action that prevents the highs or lows from becoming worse. I enjoyed using mt CGMS for 8 months last year and had far fewer highs and lows. Then my insurance situation changed and my CGMS is no longer covered. I cannot afford to continue using it. Medicare will not cover a CGMS. Maybe they don't because they know they are not that accurate, like you said. They are very useful, even when they are not always accurate, because of being able to see the trends.