Looks like an article written by a dude wearing tighty whities in his basement.
Expansion comes into play, not backpressure. The expansion helps scavenge the gasses at low to mid RPM from other cylinders from the next exhaust event (think Y pipes and equal length headers) but they also can't expand too quickly as in a dumped exhaust. In the end, that setup is causing a loss of low to mid end power but an increase of high end power which isn't good for daily driving. Keep in mind that I'm talking about fully stock engines.