This is not even close to true. ATC radar regularly loses small planes on 'primary' radar (primary radar being pure radar), and has to rely on the transponder.

This is not even close to true. ATC radar regularly loses small planes on 'primary' radar (primary radar being pure radar), and has to rely on the transponder. There are many areas where you simply don't have primary coverage, especially close to the ground. I've flown through military controlled airspace where they lose radar contact with me in a Cessna less than 10 miles from the base.