Unlike Pranic Beasts that had to go through countless variables in order to reach the end of the Pranic Beast Path—the Mystic Grade—to become a Transcendent, Free Humans only needed to reach the 10-Life Stage, irrespective of their Grade, and they had a fair shot at the Transcendence Stage.
But simply becoming a Transcendent wasn't enough. The Free Human had to gain all three Natures. Only then will they attain their true potential. This was the Brimgan Founder's plan, which was the reason he created a refinement cultivation technique such as Gold Kinesis Art.
The body and soul aspects of the power system wasn't known back then, so it was never a point of focus. However, as long as a Free Human has three Natures, they'll be strong enough to kill a higher Grade of existence that only had a single Nature.