Mr N, your intelligence services were not alone in over estimating opposition hardware. If they assessed the opposition was wholly inferior then the military case for upgrades and new designs would be weakened.
Remember the Mig 15 in its day was a world beater. The F4 was superior to the Mig simply because it out classed it with missiles, endurance, refuelling, performance, equipment and two crew.
In a 1v1 in a merge advantages dropped to fuel and a second pair of eyes.
A contemporary US int report said "one 360 deg orbit thrown sufficiently far out is sufficient to abort the average GCI."