Agreed. There is absolutely no reason they couldn't have had Deb find out. They even could've had roughly the same ending to the episode. Lazy, predictable, writing by a show that's gotten too comfortable with it's success.
I would hope you would agree, after all, Joe Washington
was agreeing with you in the first place, which effectively means you're agreeing with yourself.
As for the episode in of itself, I quite enjoyed it, no big payoff and all (outside of Deb choosing to let her personal feelings override her professional responsibilities to hand in the vigilantes).