Yes, I know... but it's like continuous fire. It's like... AA guns, with fighter jets attacking the bombers. The AM field is all around them. Sure, the magic can survive, like... a very short time. It's like quickly replacing an AA gun with another. One gets bombed, then gets replaced. Same thing with the fighter jets. They would also have a hell of a rate of fire, too, enough so that it seems like it's a constant blow. Better off leaving the bombs back at home and not wasting them.
For the IAM fields, it would remove all of the magic inside the person, too, so there would be more AM stuff in the person than there is magic. The person wouldn't be able to use his or her magic all at once anymore.
With enough magic, I guess it would work, but even then, that would be a short amount of time.