When Corey heard Pamela's true reason for choosing to stick with him despite the clear disadvantages, he felt more at ease and less suspicious since she was right.
He had also thought about it before coming to the Chained Firmament, and even after seeing so many Tier 6 beasts and the aura of beasts that could be called Half-Step Tier 7 beasts.
He had never faced a Tier 7 before, and the only being that was Tier 7 and he faced was the Throne of the Shattered Dimension of the Old Ones.
But since he was basically trashed around, and the Throne had not taken him seriously in the slightest, he could not use that to measure the power of a Tier 7.
He had planned that if he ever encountered a Tier 7, and he felt that it was unbeatable, he would run. Run as fast as the wind, and survive no matter what.
Another thing that gave him the confidence to survive was his newly acquired Gravenheart Armor, one of the rewards he got for defeating Death and completing the system trial.