I can of course fly my plane at the same RPM on the front or the back of the drag curve and get very different performance.
Hanging it off the prop at high RPM and a high angle of attack can give me straight and level flight at a very low speed.
Flying straight and level at the same RPM with a low angle of attack I will be going much faster.
In the first case you will need to apply more power to get the RPM than in the second so the suggestion that HP and RPM are directly related to each other is wrong.
Stuff the nose down and watch the RPM increase. Is the engine generating any more power to produce this increase?
Pull the stick back and watch the RPM decrease. Is the engine producing less power?
Mike
Lots of barking - wrong tree!