I get the impression that the swordmage is only proficient in light armour, and to use this ability they only can use 1-handed weapons. I have not made the comparision using the best possible light armour and this ability, vs. other classes using the best possible heavy armour such as +6 Godforged Plate with a shield.
Taking the hypothetical 30th level Swordmage with 28 int into account.
10
+15 AC from level
+5 Elderhide armour
+6 Enhancement Bonus
+9 Intelligence bonus to AC
+9 Swordmage warding int bonus
+1 armour specilization (hide)
=55 AC
The hypothetical 30th level Paladin into account.
10
+15 AC from level
+14 Godplate armour
+6 Enhancement Bonus
+2 Heavy Shield
+1 Shield specialization
+1 armour specilization (plate)
=49 AC