If Yang Kai had assumed his great dragon form, he probably could have killed the territory lord already, or at least make it so severely wounded that it would be good for nothing. However, that's not really Yang Kai's style because he always wants to use the minimum power to battle opponents, to gain the maximum amount of battle experience from the fight. He's now fighting a war that has lasted for thousands of years and costed tens of thousands of precious human powerhouse lives, but he's still more concerned about every second of his personal growth as a martial artist than the benefit to the big picture. So, never mind killing a territory lord if he can't learn anything from it.