"Does anyone complain that you cannot create a de facto "no drive" zone of T3 land units? PDs are horribly inefficient, and their inefficiency is integral to the balance of the game. Turtling must always be less efficient than attacking"
You CAN create a no drive zone with PDs, Artillery and such. And you have so much stuff you can choose from to realize that!
Turtling shall not be less efficient. You can not turtle in every direction and the enemy has to look for a weak spot.
With planes you can always look in the whole base when you have enough planes. Does not matter how much AA you have.
And you dont have that much of a reservoir how to defend your base against air attacks....