Can you elaborate on this? Is it more or that you have something against the character in general or just specifically the idea of him being used in this particular movie?
Nightwing is a complex character. He's a complicated character that noone knows unless you have some familiarity with batman canon
So to put him in this movie is robbing him of the correct amount of fleshing out he should get.
There shouldn't be a robin or nightwing because this is a superman movie with batman in it. Those are batman characters that belong in a batman movie. This movie should be about batmans relationship with superman and against whoever the villain is
Lex Luthor is another incredibly complicated character. So you have batman, lex, superman all incredibly complex characters
There isn't room for other people. Bringing in other heroes will lead to hawkeye syndrome where the character is one dimensional.
The only two extra characters id be ok with are flash or wonder woman but only in a bit role kind of introducing their presence in the world but not really a part of the movie at all because those two are potential franchises.
Nightwing isn't, he's a supporting aspect of the batman world. And he should remain there