Well, imo, I was mainly thinking about how moodier and darker Bruce has become after Jason's death and Barbara's shooting. He made Dick become Robin partly so Dick can deal with his own grief and provide him an outlet so he wouldn't become a darker person but with Cass you have something darker mirror image, an emotion-less warrior who is wholly dedicated to the mission. Frankly, I think he would have taken a different but similar route to what he did with Dick basically introduce her beyond the world of crime fighting and that might force him to come out of his shell a bit to do that.

Of course I'm not trying to downplay Alfred's or Dick's role in the Bat Family dynamic just pointing out how in the Bruce/Cass relationship, it could have been Bruce being the one who has to lighten up someone else this time instead of the other way around.