If the guy has a load of airships then he is less likely to have loads of defensive troops as well defending the city, and vice versa, if you are not strong enough to take a city with some air ships then you are in trouble wether they are using airships or not.
I agree they are broken and like in my current game they are a pain, but my stack is big enough, promoted enough, and advanced enough so they are a definate annoyance but not a stack breaker, its nice to march in and know 6 airships just dissapeared.
I would also like them gone from the game however, or dramatically changed, I thinnk a thread some time ago suggested a reconisance role rather than aggresive one (sorry for the spelling not my strong point)
as always if there is a problem take more troops..