The Blood Pool in the Blood Moon Territory guarantees a substantial amount of experience with just one dip. As such, when Zhou Tian was lucky enough to get in once and even used some of his methods, the benefits he gained were naturally astonishing.
In fact, Zhou Tian had already acquired several new skills from the Blood Pool. He chose not to use those skills all at once simply because he planned on tricking the Bone Dragon. Undoubtedly, given the current situation, it was evident that Zhou Tian's plan would not have any issues being executed.
If Zhou Tian had unleashed all his skills at once, he could have dealt significant damage to the Bone Dragon. But considering their distance and the effect of the undead monsters, if the opponent turned tail and ran at any hint of trouble, Zhou Tian would not have been able to do anything about it.