Very few demigods were actually enslaved after they became demigods. But the point remained that what Legion was doing was not strange or new.
They were not the only ones doing it. So more than half of the people on the battlefield were following the orders of other demigods. This made it difficult for Legion to advance after a while.
Whenever they struck at someone who was in league with another demigod telepath, this person would call for help, which would make the fight more difficult.
The helpers that were called slowed down Legion's speed of victory and prevented them from using their brainwashed telepaths to gain a quick, overwhelming victory.
Not only that, but this situation also increased the pressure on Legion to remain hidden because more enemies were paying attention to what they were doing. It didn't stop them from making progress.
