Lex Luthor for one, Joker had no powers and he believes he's in the right. I kind of want to include Kid crusader for a more obscure reference. There are others, I'm not very well informed on Marvel though.
Supergirl is still a teenager and Petey dating her seems awkward to me. In my opinion Oracle or , and hear me out, Huntress. Helena is capable of defending herself, which is a plus, strong spirited, and values education (she's a teacher). I think they could work.
What can Steel do to harm Citizen Steel? CS has shown great strength (above earth 22 Superman) and he has high invulnerability. I could see a stalemate if Steel stays in the air, but since Steel needs to kill Citizen Steel, he might have to get in close and then CS would have him. Also, I don't think this could affect much, but maybe CS could throw cars or debris or something since its in Metropolis. Just an idea.