It does not scale linearly. Your powers also do not scale linearly. But yes, it does spike a bit at the end. It’s meant to be challenging.
Oh wow. Why is it so low? Oh right, Layer 3. Well, that sounds manageable if your HP is somewhere on the upper end of the 100-200k range by that point, which it will probably need to be to beat the boss anyway.
Just relax dude. Yeah, it’s more difficult than regular Torghast. Enjoy the experience of learning and trying to overcome it, if that’s fun for you, or I guess just group up and cheese it.