Crystal of Protection, the light damage comes Not from a Holy source, it is he bundled light cause the damage. I think light damage does not have to be 100% just Holy but most is.
But, since he is called Crystal of "Protection" is better to give him to the Holy School.
Dragon's Breath comes closest to Shattering Wave.
Dragon's Breath 12 Mana, Level 3, Range 0-3, 4 Damage + up to 2 Burn, 2 Targets
Shattering Wave 8 Mana, Level 2, Range 0-1, 3 Damage + Critical Damage, 2 Targets
If Shattering Wave would have the reach of Dragon's Breath It would be definitely too cheap, but 8 or 9 mana is the right cost for it i think.
The Ranges are also a considerable part of the mana cost.
It would certainly be different if it could be used against Resilient creatures.