I have a tech and the only thing with which I've been making reasonable headway is Overcharge. But if I spend one round on Deflector Regeneration, so that the shield holds longer and I don't run out of energy, that's a round in which I don't make headway and can be stunned.
Also, the fight is of course being made extra-difficult by the fact that you can't simply leave and change your equipment.
Frankly, I can't think of any other fight in any of the other games that has brought me that close to simply quitting the whole game. Heck, even if I think I never actually managed to win the final fight with Lethice in CoC, at least I know this is the big finale, I've seen most of the game and grinding a bit more might improve my chances (for which I then usually don't have the patience). Here, we're talking about a dungeon boss, and looking at the thread here, there may be yet more frustrating fights in store.
So maybe someone think a bit about the balancing. Even defeating the juggernaut feels hollow if immediately thereafter, you get completely shut out and stomped.