Actually Dyson usually rates far higher in consumer tests than bagged vacuums, and it usually rates slightly higher than most bag-less vacuums.
Vacuum ratings are generally low to begin with, yet still get purchased. All portable vacuum cleaners fall flat on their face in terms of convenience compared with central vac, however not many people are stupid enough to pay thousands of dollars for a slight improvement in convenience.
Having had both central vac and a Dyson luggable, I vastly prefer the Dyson. Carrying around the 30 feet of tubing for the central vac was hardly convenient at all.
Vacuum ratings are generally low to begin with, yet still get purchased. All portable vacuum cleaners fall flat on their face in terms of convenience compared with central vac, however not many people are stupid enough to pay thousands of dollars for a slight improvement in convenience.