I did like how Nightwing dressed down Arsenal and how the new kids balked at joining Young Justice. If the show had not been canceled I wonder if they would've formed their own super team, this universe's version of the Titans, Outlaws, or Outsiders?
I didn't care for Nightwing's reaction. As he said himself, the time for that is when they get back to Earth, not in the middle of combat. What if he drove Arsenal to do something even more rash?
And you don't chew out your subordinates in public. Bad for morale. He might not have lost the new kids otherwise. I wouldn't want to work for such a jerk either.
Nightwing has a lot to learn about leadership. The business with Aqualad and Artemis may be another example, though I'm still trying to decide if he was wrong.