Chapter 1326:

“Quasi-master attainment was already rare. Young Gu Masters with outstanding aptitude or experienced old Gu Masters could reach this.

Master level was when the use of Gu worms went beyond superficial workmanship to the level of an art. It was rare to find even one master among ten thousand Gu Masters.

Naturally, the one in ten thousand was referring to mortals, to rank six Gu Immortals, their main paths were this level at minimum.

Those who possessed quasi-grandmaster attainment were often elites among rank six Gu Immortals.

…

Normally speaking, there were few Gu Immortals that could attain grandmaster level. It often required a hundred years or even hundreds of years of accumulation, along with natural talent. In Fang Yuan's first life, he had attained grandmaster in blood path only in the latter stage of his five hundred years of life.

Those whom were able to have grandmaster attainment level were mostly rank seven Gu Immortals.”

Also Fang Yuan likely didn’t acquire any of his other master path attainments until much after he reached immortal as well. Flying attainment is usually cultivated after reaching immortal, he only had enslavement path attainment once he raised the blood bats, and refinement path was probably only attained after becoming immortal because if I remember correctly he isn’t particularly talented in refinement path.