This battle was not one of physical might. While Walker knew that he could charge at the immortal king and deal massive damage to him using physical strength and the eternal orb, he was completely unable to move.
The mana around was forcing him to focus on just stopping it from running amok. The immortal king had shown his hand. Had shown how he had emotions that were not just cold and hateful things. He was actually sounding like a normal person.
One that had been scared and broken by the things that they had lived through. If Walker was not knowledgeable about the evils that the immortal king had committed, then he might feel bad. His heroic side might even wish to help him.
Luckily, Walker knew it all.