I don't consider flying an ILS to be any different from a visual approach.
The only difference is the cues used to confirm centerline and approach slope.
Thus as I have done since I was a student, Attitude controls airspeed and power controls rate of descent.
What happens when people start IMC training is that there is no revision of the secondary effects of controls including power.
With regard to the pilot unwittingly gaining 400ft trying to slow down for the hold, what is different to slowing down in the circuit?
People who claim to use power to control speed are not adjusting speed in isolation.
To explain, if the aircraft is on the glideslope but a little slow, the pilot increases power and the aircraft accelerates. If the pilot does absolutely nothing else, this extra airspeed will cause an increase in lift and the aircraft will rise above the glide slope.
Thus probably unknowingly, when the pilot increases power to accelerate, they reduce the angle of attack (reduce the attitude) by moving the control colum forward slightly to keep the same amount of lift at the new higher speed.
Power + Attitude = Performance
Works in every situation for me.
Regards,
DFC