Theres an obvious reason why this is balanced, the lack of points neccessary for this skill to be effective makes it balanced. With maximum points in Protection Shield of Regeneration will typically be a better choice, but Shield of Deflection offers 6 seconds of protection with 0 points in protection magic, providing 50% deflection, which is the same as Guardian with 14 or 15 points in Protection.
Top that with roughly 25% more blocking then Guardian througout, and added armor, and you have a pretty impressive Elite, with high points in this skill you will have so much deflection, that You will take 1 out of every 4 hits, even with 4 melees attacking you, your likely to survive, then you put on armor, which is enough to ensure that if you get hit, it isn't going to hurt, and it also protects against elemental damage. With a recast that can ensure that you can continoually recast this on a target until you run out of energy. 6 seconds is plenty of time for the skill to recharge and recast, because of this enchantment stripper will waste their skill striping this because it is a spamm skill.
If this was a 5 energy skill, and you include the obvious healing it would get from divine favor, a Monk could negate everything but degen and armor ignoring damage on one target, with the addition of other spells casted in between Shield of Deflection, it would easily make 1 teammate invincible, and it probably does, which is why having it cost 5 energy would be totaly broken, 5 energy recovers too fast, not including regeneration support, and with high points in Divine favor, and maybe even boon, you would have a broken spammable skill which allows you to heal, deflect, and armor your teammate constantly for a very long time. With 10 energy cost, the amount of defense is balanced, and it will be "hard" too keep this spell up indefinetly, although it isn't impossible with uber energy support.