A missing Heavenly Dao Fat Ball + "Heavenly Dao Completion Plan" + a Daoist willing to sacrifice himself to complete the Heavenly Dao = two Heavenly Daos existing in the same era.
However, in this situation, while both the "Heavenly Dao Fat Ball" and the "Daoist" are considered the Heavenly Dao of the 8th era, they didn't achieve enlightenment at the same time…
Moreover, the Daoist's ability to attain the 8.5th era's immortality hinges on the "Heavenly Dao Fat Ball" being gone.
If the Heavenly Dao Fat Ball were still alive before the ritual was completed, the Daoist's sacrifice to complete the Heavenly Dao would only serve to perfect the "Heavenly Dao Fat Ball," essentially sending a lamb to the slaughter and filling in the Fat Ball's missing parts to make it a perfect sphere!
What Song Shuhang and Senior White want is for "two different entities to achieve immortality simultaneously," so they can't follow the Heavenly Dao Fat Ball and Daoist model.
