"Any advance of your enemy into a territory with fewer AA units than Artemis actually becomes a gamble, requiring him to be willing to abandon his units."
To be honest, I'm not sure exactly what you meant (perhaps you used Artemis as an analogy), but I disagree that Artemis is a good counterargument against magpies. Her rocket costs 100 resources, exchanging for a relatively cheap magpie and having a chance to simply lose all charges on weak units and miss a key attack.