conceptual chaos: momentary vs steady state
One doubts you'll get clear resolution of this one, either with your mates or on this forum. Even in the few posts thus far, we're beseiged with references to "it" and "this" and other vague substitutions--we can't really tell who's referring to what flight regime or how long that regime persists or . . .
The first thing to get clear is, perhaps, the distinction between transitory effects (as in pulling BACK on cyclic, causing 20-90 second increase in RPM as rotor disc intercepts more air at same airspeed) vs steady state conditions (stabilized descent, constant cyclic/collective positions, constant airspeed, thus constant RPM).
Draw diagrams. Sketch graphs of RPM vs time. Establish that you have common points of reference. Be specific.
An interesting corollary conversational practice exercise in a less technical, easier-to-demonstrate arena: when you perform a turn on a bicycle, which way do you first turn the handlebars? [Answer: AWAY from the direction of turn. Very briefly. Because you FIRST have to establish the bicycle's angle of bank, disrupting its balanced straight-ahead motion, and THEN you turn the handlebars into the turn to maintain angle of bank, and balance. But nobody actually LEARNS it that way, so they never have to think about the details!]