I don't understand why drones must inherently have limited ammunition or bomb payloads. Just make the same big beefy airplane you were going to, but instead of having a human fly it by wire, have a computer fly it by wire. Outfit it with more sensors if necessary, but I suspect modern fighter jets are pretty well decked out in that department already.

The only thing I can think of is creative solutions to incoming missiles, but if that really is something that computers cannot currently do, I doubt that will remain the case for long.