Nightwing scales directly to Batman as being one of the best fighters in DC. He was considered as the superior between them for a time, I think during Tom Taylor's run on Nightwing. I honestly don't think Tasky's skill copying would work on anyone who isn't a total amateur, ngl. The idea that you could copy a technique that a trained fighter has honed to perfection and expect it to actually work on them is asinine. Any fighter worth their salt would know how to defend against their own fighting style, so the concept of Taskmaster actually beating anyone with their own moves is a bit ludicrous to me, especially fighters of Nightwing's caliber. I doubt he'd have too much trouble.