Since the Great Lion had put it that way, Xi Wei did not hold back and took the divine fragment of the Lord of the Peaks.
He had more or less sensed then that Aslan was consciously grooming himself.
While he didn't know the Great Lion's specific reason for doing so, it was perhaps to strengthen the Invisible Pantheon's overall strength so that their cabal would gain more authority amongst the gods, increasing their odds of survival if a divine war really kicked off.
After all, the Great Lion seemed to have been shouldering the Invisible Pantheon on his own, and it made sense that he would find it hard to keep things together by himself. Moreover, Xi Wei had the greatest potential to improve amongst the other gods, which was why it was normal to develop him.
And once Xi Wei returned to his Divine Kingdom, he began absorbing the divinity fragment of the Lord of the Peaks.