The reason that Reign could hurt Supergirl is very obvious and missed by so many, Reign was created by a religious group and has magical properties attached to her powers, like her cousin Superman, Supergirl is no match for Magic. Call Zatana to fight Reign or Dr Strange, they will have better luck.
I would’ve loved it a lot more if Lena and James didn’t kiss. They have no chemistry. James also always judged her for her last name. He never really trusted her. I think the two of them kissing was a big mistake. Other than that, everything was great!