Yes, but since they didn't move or attack you directly (lamia's would bump into you if you were careless, but wouldn't chase you), the half damage made sense to keep you from just destroying them in an instant. It created a nice sense of urgency when trying to save your friend.
If you were lucky, you could have your attack free your ally and then you'd have a few frames before the still-helpless ally just got scooped back up to deal some real damage.