The years she spent as the co-lead in BoP makes this factually untrue. She wasn't a supporting character in that book any more than Dinah was. Babs drove the narrative at least as often, if not more so, than Dinah.
Babs in a chair does mean she won't be on the front lines doing the kicking. That does not mean she can't have a leading role. It just means her narratives have to bend a little differently than the usual comic book character. Which isn't a bad thing.
Of course, there's also no reason why she can't be Oracle and still doing some kicking too. The role is not dependent on the chair.