So you call in question the theory of common mode filtering? There are millions over millions of these common mode filters arround which work exactly like that.
Absolutely not, I do not call in question common mode filtering of signal and return.
I call in question common mode filtering where no common mode exist, such as when one of the filters is
a) bypassed by both sides connected to ground.
b) the same coil 'filtering' both power and signal.

Erik