Hey, I only use airplanes for suicide bombing, because I hate the downtime if you have to fly to the resupply point and back, again and again. I would prefer it if the resupply simply happens after some time. Could be the same time it needs to fly to the resupply point and back. Would also encourage to use the MG more against infantrie. And it would be more fun for Anti-Air-Gunners.
You also could keep both systems at the same time. Make resupplying with timer take longer than resupplying at resupply points. This way both player types are satisfied and those who fly to the resupply point get the time advantage and the height advantage additionally.