Reworking Arcane Defiling

I'm currently running a Dark Sun game in 4e. One of the merry band of miscreants is a Defiling Wizard. Now, since they all went into it knowing that having a wizard in the party would cause some trouble. (And I'll be honest, the player of the wizard is playing a shade north of evil character to the hilt, and it's hilarious.), I want to make sure the wizard stays useful. The RAW arcane defiling power is.... underwhelming. "All allies within 20 squares take half-surge irresistible necrotic damage.", for a reroll of the attack or damage roll. Not exactly fear-inducing material. Here's what I reworked it to:

Arcane Defiling

Arcane Feature

You draw on the nearby life energy of comrades and enemies alike to fuel your spells.

Encounter * Arcane, Necrotic, Implement
Immediate Interrupt                 Close burst 5
Trigger: You use a power with the Arcane keyword.

Target: Each creature in burst
Attack: Intelligence vs. Fortitude

Hit: Intelligence modifier necrotic damage.

Effect: For each creature hit by the burst attack, you gain a +1 bonus to the hit and damage roll of the triggering power.

Special: You can use this power as a free action when you use a daily or encounter power with the Arcane keyword.

Now, it's far more powerful, and tactically not shooting the party in the foot. Well, not as much, at least. I'm sure it breaks the math for expected damage per turn or combat a bit, but considering I'm typically running encounters a bit overpowered, it all balances out.