Nightwing isn't as bad as we make him out to be, but not as good as everyone else thinks he is. Other people see his plus frames, air control, brilliant zoning (MU dependent) and amazing mixups. Nightwing mains see a poor jump arc, lack of staff mobility, lack of interactable control, fuzzy-able mixups, and meter-dependent zoning. Nightwing is a character where if you don't know the MU you will lose, even in his 3-7s, because you'll be thinking "WTF is this shit" as you get caught in his frametraps and zoning; whilst if you do know the MU, the Nightwing player will find his even/disadvantage MUs much more difficult. Personally, I think that Nightwing is a solid mid-tier character, but the mindset of the tournament players is "Why would I use him when there are tons of other characters who do what he does better", which is a completely true statement. Why spend money just to go out to a pocket Superman or a pocket Lantern?
>TLTR<
So my answer to your question is Nightwing is neither particularly bad nor good in the current meta. He is an example of a character who is very balanced and could easily be high tier, if not for a few things holding him back.