The secret this encounter is simple, either 1) find and use an exploit or 2) don't accept the quest.
The line of quests leading to the final battle is hardly a challenge. Any class can walk through the trash packs or completely avoid almost all of them if they choose. Not once did skill play into any of the minor encounters leading to the final meeting of Vox. However, for the second time in this area, we encounter a final boss that is completely immune to every form of CC available (the first is encounter during 'Defeat the Alchemist' from the quest chain Plague Bringer - which I still have to finish).
Now, as a VR2 Templar (melee/heal) with all three class skill lines completely unlocked nearly every skill that I normally have in my bar incorporates some form of CC. Just to demonstrate to myself how poorly these encounters are designed I first tried employing one skill and then for fun let the boss kill me (counting the number of attacks it took for them to put me down. That number is 2, or if the RNG gods deem it 3). Here's a list of skills that have been effectively neutered by the development team in a screwed up attempt at making a difficult encounter: 1) Biting Jabs (knock back/interrupt), 2) Reflective Light (snare), 3) Blinding Light (blind), 4) Eclipse (reflect single target spells), 5) Binding Javelin (knock back/down/interrupt), 6) Wrecking Blow (knock back/down/interrupt), and 7) Brawler (bleed effect).
This is not how you create a fun and challenging game that "you can play your way". And not the type of boss you place at the end of a solo line of quests. As someone that has soloed very world boss in this zone I just can't understand the development team's line of thought. And as though they will ever read this, I'll say this: THIS IS NOT FUN. This is is a lazy attempt to interject difficultly into the game - simply poor level design and poor execution on the concept. This fact is echoed in nearly every major review of the game so I know you know it's a problem.
As a final unfortunate note, it seems to me that finishing both side quest lines are necessary to advance the main VR quest line. So, the message once again from the developers is this: 1) you can't play your way, 2) you are not a hero in this game unless you do it our way, and 3) in general, if you can't find an exploit you're screwed.