Phantom Demons and Sword Demons were two different types of styles. Their skills were chosen based on whether the Ghostblade wanted to mainly use Sword Skills or Ghost Boundaries. In terms of PvE, Phantom Demons were actually better than Sword Demons. But in terms of PvP, Sword Demons were clearly the winner. This was especially true in a 1v1 PK, where Phantom Demons were publicly accepted as a weaker class. Even for Li Xuan, the user of the number one Phantom Demon Crying Devil, he rarely came out during the Individual or Group Competition.
This wasn't an issue of mechanics. It was simply because the class wasn't set up for duels. Anyone who was able to join the pro scene wouldn't be bullied easily by anyone, which was why, even for a Phantom Demon master like Li Xuan, even he wouldn't play a 1v1 match against one.