Remember lads, the monk looked broken on paper too.
A little correction for you, armor specilization and shield specialization do not stack as they are both feat bonus' (I'm going to put a bet this will be one of the most overlooked mistakes in 4e), so 48AC for that highly defensive paladin making the hypothetical swordmage +7 AC betterI 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

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.