Well aware! Heat alone takes much longer to clear windows. My suspicion though is that the heater will be a much easier fix. Please correct me if I'm wrong though?The real power of defog is when the A/C is fully functional and can dry the hot air as it blows.
I would even go so far as too say that A/C is more important than heat in defogging windows.
On a newer car, try turning off the A/C when the defog runs (if you even can). You will see a major drop in performance.