Creating an air based counter to asf means sams reign supreme in the late game. Asf blobs are useful as meat shields for strats and t4 air units, now that just makes it so that those units are virtually useless if enemy has sams and are taking away options to end the game. Not to mention a unit that kills asf blobs would also wreck a group of strats coming in.
You do realise that if your opponent is fully coverd in sams than it means he spend a lot on it and the game just progress into even later stage at the game. Its like asking for still having an option to kill acu with mantis on t2 or t3 stage.