I don't quite agree here.
-Archmages ignore the wall penalty.
-and the main thing about the box is that it should be at the beginning; after that, there are still an infinite number of shots.
But otherwise, I completely agree! The Swamp is a tank. Attacking it without super magic is like courting death!
But why does it necessarily require super magic? Good fighter skills and a good army (like the canned angels and the bees from the Hive) can easily handle it without magic, if the player playing as the Swamp hasn't leveled up much and has only focused on building an army and economy.