...but from Cass's point of view, he WAS a perfect father figure. He gave her something to believe in, something to be other than a killing machine, and he didn't shoot her whenever she fucked up.
You've gotta remember, the girl's got some serious issues from her upbringing, no matter how well-adjusted she seems at times. Bruce Wayne may have been the worst father this side of Cobra Commander, but he was still a huge upgrade compared to David Cain.