Change to Necromatic Corruption
I agree that it does need a change (though I believe Bone Fiend has a 19% chance to remove a boon, 1% chance to remove two, when it attacks due to the double-shot nature). Right now, Death Nova does far and away win because, as my charr puts it, “they’re so disposable.”
I think the boon stealing would be better. One, it may take advantage of the boon duration in the Death magic trait line (though in that case, I’d suggest that it applies a set boon, rather than stealing the one), two, having the AoE healing might be too much sustain for the necro himself (since he’s probably running Vampiric Master as well).
The current way “stealing” works is it copies the duration, just like Epidemic’ing a 10 second Bleed copies that 10 second bleed (no condition duration bonus).
But I do like the idea of it applying set values, maybe applying the same boon that was stripped, but at a set duration? For example if you strip any boon, it applies that same boon AoE for 2s. So even if you corrupted a 30s long protection, they’d only get 2s (and thus would limit anything super strong, like stealing a huge stability duration off an elite).
As for the healing, it wouldn’t add much to the Necro. Assuming even the highest amount I put down which was 500 (with really high investment from healing power), that is at best an addition of 100 HP/s, assuming your minions are all auto attacking constantly, never missing, and the enemy always has boons on to corrupt. I do see your point though.