You are 100% correct on the exhaust scavenging theory from the exhaust
valve/ port area Dennis.
However, in an exhaust system that relies on a converter with pin hole
sized passages for the exhaust to flow through the reverb effect it
totally lost and the efficient extraction of the exhaust gasses from the
cylinder's is lost.
Put the brakes on the exhaust flow with a  plugged, half plugged, or
even in good shape, with the tiny holes the exhaust gasses have to flow
through to get to the other with the converter in the way the reverb
effect gets lost in a non performance style system.
This is just the way it is.
Removing the stone from the converter alone will decrease the
restriction in the exhaust and allow the engine to breath, and perform
with ease.
( A Lot better than with in place and in tact anyway )

RC