"They need to level up more if they want their group assault on the Guardian to succeed."
They only have three ways to achieve that. Either go to lower floors and grind for centuries, kill the other Kings to take their experience, or kill the people of this floor since they also gave similar experiences because of being from this floor.
It was clear that they weren't going to kill other Kings since they needed a team and as many people as they could to take down the Guardian. By killing a King, they could definitely level up, but in the bigger picture, that was only going to reduce their combined strength.
As for the option about going to the lower floors, that was too time consuming even for these people.
"From the strategic point of view, it does make sense that they want to do this. Unfortunately, they don't know one thing..." Azekiel could only shake his head at their lack of knowledge.