I wouldn't say there was anything cruel about the work the elephant is doing, even if the Corsair is "well over four tons".
It is easy enough to roll a substantial weight on wheels, if it's on firm ground or pavement. The ground around the Corsair certainly appears to be quite firm.
The Corsair wheels are large enough diameter to provide low rolling resistance, and no doubt they are inflated to a reasonably high pressure.
I would be very surprised to find if it took more than about 300-400 lbs force to move the Corsair, with the major effort required initially to overcome the inertia from a standing start, and with a much lower pull effort required, once the aircraft was moving.
I would have thought this amount of effort would have been easily achievable, even for a small elephant, as a single draughthorse is capable of up to 400 lbs of initial pulling effort, and a constant pull effort of 200 lbs.