Leon was skeptical at first. He wanted to clear floors as fast as possible, but there was a catch. He shouldn't overdraw himself. He understood that after multiple failed attempts on the lower floors. He needed to devise a proper plan, strategize and enhance his abilities before fighting a higher-level monster. Rest was also an important factor in a fight.
He decided to hold the excitement for a moment. The mission said that he had to face the Hobgoblin King and his royal guards. So the number of enemies was greater than one. The second thing is that royal guards didn't signify any particular type of goblin. It could be a knight, or even a mage, or a special type too.
The last concern was the area in which the final scene took place. If it was a single room, he wouldn't have the luxury to bait and kill his enemies like earlier. He might need to face them directly. Which was a huge disadvantage to Leon's fighting style.