Gu Zhen Ren
Didn't spectral soul surpass fang yuan in this regard? He achieved all paths great grandmaster didn't he, in addition to supreme soul and presumably supreme food. In that sense, since the sovereign body originally belonged to him, didn't spectral soul very nearly achieved eternity? Fate was so desperate it sent an otherwordly demon fang yuan into the past 500 years to contest the sovereign body, meaning fate was absolutely in horrific state. Delaying convergence 500 years, great grandmaster all path, sovereign immortal body... spectral soul might well have been stronger than when he was a venerable at the heights of the first timeline pre rebirth, especially given he had been one of the strongest venerables before.
Spectral Soul achieved omniscience and omnipotence, but unlike FY being a complete otherworldly demon, being in a situation without Fate Gu, with no SCA interference - FY has better potential. I'm thinking Verdant Sun is necessary to refine Eternal Life gu as the hairymen had once set their eyes on, this is why Spectral Soul turns his attention towards him erstwhile.