Hi Joe,
I had a similar experience after trying different prop on my plane. Initially I used an APC 20.5x14W and the plane had great power (Vanquish, torque motor), but I was a little concerned about how warm the motor was getting. For grins, I tried a Xoar 20x13 (electric) and found that the motor response was smother. If anything, it would spool up a little faster. There is a 2oz different in the weight of the props and it had never crossed my mind that the prop inertia would have such a significant effect (the prop being a little smaller might have helped also).
Power consumption went down a little, but on windy days, I have to lean on the throttle a little harder.
Teo