Personally, I think 'Killing Joke' was a terrific story - it just had unfortunate long-term consequences. Still, we're probably lucky - there are certain characters that just don't work outside the eras they were created in. I'm not saying the Babs Batgirl is one of them, necessarily, but given some of the stuff that was being written in the 80's/90's, I can imagine some mightily heinous things bein' done to her if she'd stayed the way she was. As Oracle, she mostly avoided that by staying largely in the background until 'Birds of Prey' started up.