Several days passed and just like Leon thought, it would be hard to teach the survivors of Las Vegas how to heal wounds. Maybe it was because they only recently started to use mana consciously, but none of those two thousand had any sensitivity when it comes to mana.
Regardless, it was a matter of survival, so Leon had to keep teaching them while he can. Potions can heal wounds, but those are expensive, and it's not convenient to use them in the middle of a battle. Besides, the more people offering support from the backlines, the more the chances of someone in the front lines dying will decrease.