Zhou Wei had Heavenly Level strength, but his power was derived from being transformed into a monster, which means that his power came from external sources.
As for Fang Yi's Heavenly Level, he had earned it step by step, slowly climbing his way up. Although he used the Demon Technique "Inverse Demon Seven Turns," burning Essence Blood and lifespan, this was still a path Fang Yi walked by himself.
Fang Yi once heard an old man say that external power could be borrowed, but the most orthodox power was from within oneself. If one's internal power was suppressed by power gained from outside, on the path of Martial Arts, one could not go far.
And now, Zhou Wei was the most obvious example; he obtained Heavenly Level power by being transformed into a monster, but his own inner strength was greatly weakened. Moreover, Fang Yi himself was different from other martial artists of the same level.
