@Weird Tales As I said before, an Imp is suppose to be a fun character. Theres a reason none of them are major villains, if they wanted to they could beat any superhero or villain in a couple seconds.
But lets ignore like you seem to want us to and instead focus on his knowledge of DC. I don't have an encyclopedic knowledge of DC, yet I know how to easily defeat some DC character. Mister Freeze = Break his mask, Green Lantern = Break their will and concentration, Zatanna/Zatara = Cover their mouth, to name three easy ones. Now imagine if we faced a villain that is harder and our team has to work together to figure it their weakness so they ca-Oh no wait, just ask the character who already knows.
You also mentioned Beast Boy and Raven are OP, yet gave no reasoning. Raven in control of her emotions(Or Raven in white) is OP. Which is why she will never be in this. Beast Boy can only become an earth native animal(sometimes the dimension/world he is on), and never can become mythical creatures like dragons or unicorns.