EGKB,
It's about getting your instincts correct.
Someday you may find the stall warner go off unexpectedly. Perhaps you had your head down looking at the map, or trying to replan in nasty weather, or diagnose a problem. Doesn't matter really....you'll have fecked up and let the speed get too slow.
If you've got your instinct to be speed is set by attitude, then your first reaction will be to push the nose down...this will happen by instinct before you've even looked up and started to diagnose the problem.
If your instinct is to increase power it might not end well.
This is why your instructor wants you to try and get your instinct to be to push the nose down for speed.
As I said, they do not want you to change pitch, then wait for a change in rate of desent, then change power. They will be happy for you to change both at the same time provided you get your instinct right.
Instead of being confrontential about it and refusing to work on your instinct, why not have some fun with it?
Have a go with your instructor, where once you get onto final, you have to maintain your approach speed -2kt/+5 kts, but you are only allowed one throttle change before reducing power fully for the flare. This will help build your instinct to control your speed with pitch changes.
If you really want to you could try doing the same the other way around later. (but best not to until you are comfortable withthe first way). ie. Hold a constant pitch, and change power for speed. You'll see that you need large power changes to hold the speed within such a narrow band.