We should soon be reaching the point where anybody playing against you will look to prepare for this. Then you crush them by metagaming the crap out of them we'll see if it might even work when defended against.

http://zero-k.info/Battles/Detail/380354

Every fac gets defender, but there's no viable hard counter. Unless you drastically prepare you've still got a decent chance to die. Swift is probably the hardest counter possible, but unless you rush it before mex they can hit your factory before it's finished, killing the swift before completion and losing you the game.

I think daggers had a good chance to intercept blastwings without getting hit by fallout. Other than that, not many things can intercept it before it's in range to hit you with debris. Most facs are forced to make defenders and hope opponent doesn't overwhelm them.

I have seen several. The defender may make cost in one shot, but it's got a lot of work to do, and it's likely you've taken some damage on com or fac, or lost mex while getting it up. Blastwings can still approach from a different direction, or opponent can build gnat to tank shots then all-in com once more.