He commands flying fortress and very easy to kill if you do it right. Get his hp to 50%, jump and pull both levers return and finish him off. Lever deactivates his healing chambers for 10-15 seconds.
The way that I did it was I stood in one of the regenerators and had like 8 spawned warriors to attack of and when he went to go in the regenerator the spawned warriors were in the way
Yes, I did it just the same as you - in the time I was playing the first outcoming "Ego Draconis" version, but I'm sure with the DKS it is also a nice strategy !
On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin, it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !