The players in the arena often were unable to understand the overall situation of the match. They had to rely on their own experience and judgement to grasp the bigger picture.
That was what Wu Chen was trying to accomplish. Upon realizing that Team Demeter had guided the control of the situation from their hands, he immediately thought to get back their healer; they wouldn't be as reckless anymore.
Team Everlasting's biggest flaw at the moment was not having a healer. They understood that, and of course Demeter would too. They could tell what classes were on the field by the attacks that flew towards them. So they might have predicted that Everlasting would try to switch a character out for their healer and use that to their advantage.
So, after telling He An to switch out with their healer, his Dawn Gunner sped towards where He An's Go Forth had been headed.