But shouldn't these fast chargers be doing much more "volume" of charges on a per-hour basis? I.e., if they can pump 3x the kWh shouldn't that somewhat alleviate the need to charge more per kWh?
No, for most people who own an electric car, its cheaper (ex. charging at off-peak, and slower) and more convenient to charge at home. I only use those super chargers on road trips which isn't my normal commute.