"Walk in a circle and keep walking!" Thorn Baron was angry, but she had to maintain her composure in order to effectively lead and issue appropriate commands for the situation.
Han Sen's arrow was a silent killer, but it could still be seen with the naked eye.
Thorn Baron's subordinates were situated in a formation that allowed them to carefully watch in every direction. If an arrow was fired, it'd definitely be seen.
Han Sen's arrow delivered terrible damage to the creatures it struck, but if the creatures were able to see it come their way, they could block it.
Unable to find a decent opening for the time being, Han Sen had no choice but to fall back. Removing two mutant creatures from the field of play was good enough for the time being.