On Defence:
Arcane [Guardian] and [Health Conversion] should be pushing you to about 2440 armor at any given moment. This is added to your 3 as health, multiplied by power strength. If I've done the math right you should have around 14,700 base health on your warding halo BEFORE it absorbs incoming fire and grows stronger.

Warding Halo will absorb 90% of incoming damage first. After that, remaining damage will be applied to your armor with ~88% DR. If you can't survive with a 98.8% reduction in incoming damage, it may be a you problem.

On Offence:
His 4 ignores nullifiers but is cancelled by Ancient Healers. Using his 2 (uncharged) on an enemy impaled by his 4 will spawn more chakrams that stack up the damage bonus from [Reaping Chakram].

Leave 1 on, use 2 to mark enemies for additional damage and to spread heat procs. Run around with a melee weapon and cleave everything for great success.