Lacivius has always been a tough one to beat because of his AOE attack.
I remember it was the same in Quest; it took a long while before any of us could pass him.
Since the patch they have upped the power of most heroic bosses and lowered stun chance.
Defense runes or talents seem to have no effect on the damage he deals.

I noticed HP, Dodge and attack does make a difference.
I do feel they could adjust him somewhat.

Good luck and the best of patience.