Devouring him would be far more beneficial than taking him as a subordinate.
After all, the Cultivation World was a place where the strong preyed on the weak. Even if Xu Lai did this, outsiders couldn't criticize him for it. On the contrary, they would say The Supreme Emperor had found a great opportunity!
That's just how the Cultivation World worked. When you gained an opportunity, someone else would inevitably lose that same opportunity or even die because of it. It was a zero-sum game.
But after careful consideration, Xu Lai chose to extinguish his greed.
Thus, the Heavenly Court gained its Tenth Divine General.
