Agreed

While I use a HR monitor I agree that training with power is the way to go. HR can fluctuate based on hydration, fatigue or any number of other reasons. If you are producing 160 watts, as an example, at a cadence of 75 and then increase your cadence to 90 watts to maintain the same wattage you can begin to find out where you feel more comfortable and get an idea of your ideal cadence.