Babs eventually proved to have the physical ability and emotional maturity for the role, though. She approached her role as a crime fighter seriously, and managed to hold her own as a result. Babs had the sheer talent to pull it off, really.
In contrast, Steph started crime fighting for immature reasons (screw over Deadbeat Dad), kept at it for equally immature reasons (Boy, that Robin is cute!) and seemed to spend more effort trying to earn respect than actually becoming a better crime fighter. For the longest time, she served as a foil to show how mature and able other characters were!