Due to their bodies being weaker than body cultivators, all essence cultivators naturally protected their bodies with a layer of Qi, to guard against any surprise attacks. The level of protection depended on how much Qi was supplied to this barrier, which constantly drained Qi from the dantian. To cultivators, this felt like running a marathon, as the drain was slow but steady.
For those who were lazy or those who looked down on their opponents, they used the minimum amount of Qi they thought necessary, as anything else was nothing but a waste in their eyes. The man that John had just slain in a single attack was such a man, who looked down on John and his power.