I wouldn't call Corban OP by any measure. He may register as high tier in several places like RPG, but outright OP comes off as a bit of an overstatement. At least when compared to other characters who I believe are around the same level anyway 

Edit: I'm actually not really sure where this idea that Corban is some OP golding comes from. He's done far less in his time here than would warrant this idea. Scrolling through sheets, I see outright city-busters o.o