[dredmorbius]

Most commercial aircraft take off and land well below their cruise speed. My understanding is that this limitation applies to supersonic aircraft as well. Applied power is typically restricted due to noise control requirements near airports.

That wing lift/drag relationship may be less fungible than you're supposing in order to address lower-speed flight segments.

[Gravityloss]

Yes, it was just a thought experiment from first principles to get a feel for the problem.

In reality, planes fly higher where the air is less dense, and faster to keep the lift and drag equal.

In a car, lift is not needed. Higher speed doesn't have compensating effects. Higher speed more clearly causes more fuel burn for the distance.

[dredmorbius]

Fair enough.

If anything, automobiles frequently utilise negative lift, as with a Formula 1 or Indy Car's inverted wing which generates increased downforces. On street cars you'll find spoilers and similar factors.

Aircraft can fly low and fast, though that's typically associated with combat aircraft evading radar or air-defence systems. Such missions are known as fuel-burners precisely because of the greatly increased drag.