The higher the quality of the first Star Core, the better the effect in assisting advancement.
There was no doubt that the top-grade Star Core cast in Xu Jin's Central Star Palace provided the strongest effect in assisting advancement.
According to Ning Yuchan's words, the effect of a middle-grade Star Core was equivalent to a normal Star Casting Pill, a top-grade Star Core's effect was equivalent to a top-grade Star Casting Pill. Xu Jin estimated that his top-grade Star Core from the Central Star Palace, when used to assist in casting the Lower Star Palace, would have an effect at least equivalent to a First Essence top-grade Star Casting Pill.
Moreover, most crucially, the Gathered Star Core that had been cast in the Central Star Palace could be reused.
It wasn't like a Star Casting Pill that was gone once used.