1 = The only direct defense, you mean. Ground control negates air attacks by a margin at the moment. (Ground control changes are being tested in the test server atm, 3%/2%/1% depending on victory type.)
2 = 10%? If so, that's a shitload of work they're doing, for a very cheap cost ($100). I would rather they do come at a somewhat more significant cost ($4,000 and 5 steel), and take down 1-5 aircraft per unit.