Some of the drop in aviation fuel consumption may be due to QFd (and VAd?) reducing the frequency of flights on some routes, as per QF's stated aim to decrease domestic flights by as much as five per cent.
You make a very important point.
While probably not an 'either/or' situation, if one had to choose one of the three fuels to restrict supply of, that'd be petrol, as especially in larger cities, many trips are discretionary and could be replaced by other modes, or simply don't travel. Electric vehicles are an available but imperfect replacement as resale value may be poor. Recharging availability, speed and type remains variable and apparently sometimes deficient.
Jet A1 is essential for connections between cities (and rural Australia) plus connections overseas with s-called sustainable aviation fuel way too expensive, while Australian agriculture (and to a lesser extent horticulture), mining (think huge iron ore and coal mining trucks), general transport trucks/ B-Doubles and efficient rail freight using dieselelectric locomotives all require diesel, with no affordable or practical substitute feasible.