Even as Jax's awareness of the outside world began to degrade with each passing second, he still knew enough to know that there was something very wrong about the boss he was fighting.
It was acceptable that the boss guarding a 3-Star ticket would be strong. It was even expected. However, this was way beyond the point of what one should have to face in the very first trial to the next realm.
Jax knew he wasn't the strongest person out there. There had to be many warriors that were physically stronger than him with their skills and spells. But even so, thanks to his great starting strength, and the incredible weapon he used, he should have been close enough to them that his strikes did something to the boss.
But other than the chink in his armor, he had been able to do nothing at all. Even his furious swing on the back of its knee had resulted in nothing other than the boss kneeling on the ground for a bit.