I think the game should have the option for you to research a "Heavy Lifter" cargo plane, which would allow you to transport a certain number of units that you normally wouldn't be able to transport by air (armored tanks/tank destroyers, radars/missile defense systems, etc).
It should be high up in the tech tree, and would only be able to transport a certain number of those units at any given time.
It should be high up in the tech tree, and would only be able to transport a certain number of those units at any given time.