Enemy aircraft like the Chunook have extremely high damage and Offense, capable of taking down multiple backline units in just 1-2 hits, even if they have high Defense.
One way to balance this would be to give AA Turrets the ability to Suppress aircraft, so disposable player backlines like Arctic Troopers can use their Defense to dodge some hits and survive a bit longer, while Nano units like Veterans actually last.
Reducing enemy aircraft base Offense a bit might also be nice to have.