JI3 will NEVER beat jump back IA wingdings unless Nightwing fucked up heavily.
It can beat neutral and forward jump wingdings, but not jump back IA MB wingdings, and as long as he saves his meter for that situation, you have to block until he uses his meter or intercept him as he's leaving the ground.
Steve0, somewhere in our archives I have a set against Sonic Lionheart's Hawkgirl that illustrates the MU fairly well (AKA I get a hit she dies, but I *might* get a clean hit once a set when he fucks up).
You are wrong about the number of Mace tosses thing though. That only applies if she uses the max number of tosses, and shooting her on the way down only works if she's at the apex of her flight, which she does not need to be to stay in our blind spots. She can throw 2, drop, throw 5 more, drop, throw 1, MB the toss when you tried to guess on a landing, go back to flying.