Martial cultivators were different from essence-gathering cultivators.
Their attacking force was mostly superior when both sides were average at their cultivations. Their pure physical might sometimes even matched that of cultivators with average essence energy, while martial energy matched their highest concentration of essence energy, so what if martial energy was condensed and used to strike?
Wouldn't martial energy have the upper hand in a close quarters fight?
Considering Gong Kim-Jin's prowess, it was quite clear that he could even fight against a Mid-Level Martial Master Stage Cultivator and struggle for some time against a High-Level Martial Master Stage Cultivator.
If he combined his Essence Gathering Cultivation which was also said to be exceptional, with his Body Tempering Cultivation, then it was no doubt that he could battle with High-Level Seventh Stage Cultivators like core disciples and even kill them!