It's also a misunderstanding.

Lower instantaneous pressure is better for scavenging. Problem is, most people think about the exhaust sytem as if it was steady-state flow. Really, the flow pulsates, and each pulse is reflected back thru the manifold to other cylinders. That either helps or hurts exhaust scavenging.

So you want a system where those pulses are coordinated to help out the other cylinders. That's often a system which has more 'restriction' if you simply test it by flowing steady-state. It takes either more sophisticated analysis or instrumentation to show that it really does result in lower exhaust pressure at the right moment in the cycle.