When Selene, Kiefer, Willow, Jeremy, Matias, Rorik, and Caesar saw Corey's struggling expression and how he seemed to be in a lot of pain, they were all surprised because he seemed to be going through a lot more than them.
And they began speculating that the reason why Corey was struggling so much was because of how strong he was.
They assumed that the pressure of the Chain of Sovereignty scaled not only with how high one reached, but also one's power.
Although they could not be blamed for having such thoughts, Corey was not truly struggling because of the pressure.
Well... he was.
But it was not for the same reason as Jeremy, and the others.
For the others, their bodies were feeling a suffocating weight that threatened to fall them to their knees. But Corey could easily ignore this pressure that could even make Tier 6s to feel immense discomfort.
Corey was not struggling because the force was acting on his body. He was struggling because the force was acting on his Will.