Stop spreading wrong informations.
It's not impossible for ANY spec. I already linked you videos for your own spec, so just stop this.
If you are not able to clear Layer 4 of normal Torghast (obviously not Twisting Corridors, because you can't get doggos there), it's a freakin' you problem, nothing else.
I'd honestly like to see how you play, because you definetely can't be playing your arcane mage to his full potential. With all this free gear (free 197 armor+cloak, 187er weapon) a L4 normal Torghast run is completely trivial.
You probably spam Arcane Barrage or Arcane Missiles instead of using Arcane Blast or Arance Explosion for stacks - or aren't always using abilities - or moving away from enemies and getting hit into the back.
I know people that played with me in Vanilla and they STILL backpaddle when enemies are in melee range to them. It's wroooong - they hit you and you do no dmg.
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The worst part is that I already linked him solo L8 (normal and TC) Torghast runs, which he completely ignored. He just wants to spread wrong informations, that's all.