by virtue of empowerment in that they have a character who -is- capable of so thoroughly derailing this strong central figure
That's an interesting idea. But it implies that the author would be for their own character rather than for the hero, if I'm reading you right, or that it'd be more about their own character than about the other. In the case of Tarantula and Nightwing, I has the impression it was about Nightwing, and specifically his reacting to another new crime-fighter in 'his' (not really) city. Like others have said, Tarantula was only pretty much a footnote in the long lists of things gone wrong with Dick's life, most of which were orchestrated by Blockbuster. She only became so important after she killed Blockbuster and Dick felt twice as responsible for everything she did.
Honestly, Tarantula sucks at what she does. I'd think that if she were a wish-fulfillement character, she'd be a little more competent a crime-fighter at least once. Instead, she's a murderer, and the first murder she committed is the reason why Dick and she can't bring Blockbuster to justice the way Dick had convinced her to try. At one point she works for Blockbuster. She's got other skills - she's good at psychology and playing with people's emotions, she fights well and she raises fair points about crime - but she sucks at long or even mid-term planning.