Coming from someone who actually *reads* Nightwing comics unlike my brother (bythepowercosmic), a show based on Dick Grayson/Nightwing would have been way more logical than Green Arrow.
For starters, more people are familiar with Robin, and could have been introduced to Nightwing through that. The show wouldn’t even have to involve Batman since the Nightwing comics revolve around Dick working in Bludhaven alone. With the exception of Blockbuster, Nightwing’s main villain, there aren’t a whole lot of superpowered characters. And Nightwing fights crime with martial arts + acrobatics which is a little more believable than a dude in a Green hoodie running around with trick arrows.
I know the trend now is the Christopher Nolan-esque “NO SUPERPOWERS EVAR!!!!!” approach but if a network played Nightwing as a crime drama with the occasionally super elements I could see it really working.