You can say that the battle between two legendary grade people was happening far away from the battlefield Warriors fighting those enemies and those Monsters. But still you can say that everyone in the battlefield can feel the impact that was created by their attack.
Both of them were each other using their full power so naturally impact like this was created by that and right now if you look at the old King then you can see even though he already became injured but the situation wasn't that serious. On the other hand, if you look at the enemy then you can see his situation was very serious compared to the old king.
First of all he was already low on spiritual energy and did not get the time to recover his lost spiritual energy. Not only that the old King also continuously attacked him so naturally he needed to differentiate himself and at the same time he also began to counter attack using the remaining spiritual energy.