HC
If you pause to think about it, how you fly, and how you SHOULD be teaching, is that cyclic controls speed and collective controls altitude at low to medium speed, but at higher speeds you must control altitude with cyclic and that leaves collective for speed.
You have confused me now - surely an instrument approach is at low - medium speed yet it seems that the way pilots fly the approach is as if it were high speed.
Being a product of the RAF system I, like Crab was taught that cyclic controlled speed and that power via the collective controlled height. The scenario you put forward of cruising at max power didn't occur in most RAF operations as the helicopter was usually been aggresively flown at low level - 50ft in German Ex areas and 100ft elsewhere
HF