Thing is, there's an achievement tied to each level cap Carnival, part of which involves taking no damage at all. So. Decreasing difficulty would not only negate that accomplishment, but also may be seen as less necessary, given that the fight is literally designed in such a way that all damage is avoidable.

It's a scripted dance. All about learning when it's safe to attack and when you need to move, where to be, how to react, etc. If you're taking a lot of damage, you need to learn why you're taking that damage and to correct your mistakes. You're not going to brute force your way through, so take your time and play it safe.