Gu Hang, having landed, was truly exhausted.
The Primal Fury Owl attempted to flee back to its own realm, its efforts to escape the interlayer of the reality veil thwarted by him. In the Evil God's final madness, Gu Hang bore immense pressure.
Had it been him before the upgrade, it would have been impossible to endure.
Indeed, even after the upgrade, it was still unsustainable.
He could hold on for two main reasons: the Primal Fury Owl was weakened by more than one grade due to being in the interlayer of the reality veil; and as a wielder of Spiritual Energy, entering the True Realm brought Gu Hang closer to the source of power, which allowed him to use spiritual energy that had been elevated by more than one grade.
With the weakening of the one and the strengthening of the other, Gu Hang was given the chance, with his mortal body, to slaughter a deity, to achieve such a great feat.