The reason why Wu Wei felt that this demigod of his was the weakest demigod in history was because he was a demigod.
It was because of his divine fire that had already been ignited.
Wu Wei had obtained some information regarding the Divine Flame and Demigods from An Lin.
To become a demigod, one had to condense a divine seed with divine power and then ignite it.
Wu Wei had done all of this, but there was one crucial detail that he did not have.
According to Wizard An Lin's [Secret Records of Ascension to Godhood], one's divine fire would undergo a transformation upon becoming a demigod. After the transformation, the origin talismans within would be able to shed their supernatural powers and become divine.
To put it simply, as long as the origin talismans of the divine fire were ignited, no matter what grade they were before, they would all be at the demigod level after ignition.