Yet only 54000 km at the more typical average speed of 30 km/h. Are aircraft engines typically under high load at cruising speeds? It would seem they are generally overbuilt to overcome the high demands of takeoff.
Highway cruising might take 20-40 HP depending on your vehicle, which is probably more like 10% of rated power. 70% of rated power in a typical American car is probably like 120 MPH.
More importantly: if your car engine dies you gradually slow down and pull over. If your plane engine dies calmly pulling over isn't an option. It's much easier to justify spending the money ensuring a plane's engine is reliable.
18K gallons will take a typical road car around 500K miles, so an airplane engine getting "only 1800 hours" of flight time likely outperforms the typical auto engine.
I'd say that's closer to going 110km/h or 65mph in 2nd or 3rd gear for most cars.