Fully Comprehended
With the last Absorption Array, William directed it to send its Mana into the Reius World Seed. He hoped that by sending Mana into his home World, William might be able to help Fria improve her real strength.
As of right now, the strength of Fria and the other Players was mostly false. Since their Soul Strength was the only thing that could truly improve, Fria was probably one of the strongest people on Reius and she didn't even know it.
If Mana started pouring into Reius, however, there was a slight chance that some people would notice immediately. Eventually, Cultivators would appear and the overall strength of Reius would grow.
William didn't care much about the others, but giving his adopted family a chance to Cultivate while protecting his sister was the ideal outcome. He was confident that any resulting chaos would be manageable by Fria and her absurd Soul Strength.