Even if Taiyi is the only one to attain Dao through three corpses after the Taoist Ancestors, so what? He bears an indelible stain, which alone makes him incomparable to Jiang Chen.
But Jiang Chen is different; not only is he the direct disciple of the Saints with pure lineage, but he also overthrew the Buddhist door, bringing back the Fate once divided to the Mystic Sect.
In other words, Jiang Chen has significant Merit to the Mystic Sect. He proclaims himself as the Immortal Emperor due to this. Tracing back the origin, Buddhism is inherently Taoism, and after this event, many Great Divine Transcendents secretly called Jiang Chen the Immortal Emperor.
Since Jiang Chen is the Immortal Emperor, who else is more suited to rule the Immortal World after it is opened?
Let alone opening the Immortal World, claiming that it can make Immortal Dao flourish is merely a statement to deceive outsiders, and none of the Mystic Sect's strongmen believe it.
