The way I think of it, Babcock isn't going to be a guaranteed cup or make the team a ton better on his own, what he will probably do is the least amount of damage that a coach can do to the team.
If we get a lesser coach that person could end up being detrimental to the team, like Berube was, but at least we know that Babcock isn't going to stop a team from competing.
A good coach uses a team properly and maximizes their effectiveness, they don't make the players play on another level or somehow make bad players gain talent. But a bad coach can stifle talent and make it much harder to win, we've seen that. So getting Babcock isn't about wanting a coach that will make the Flyers instant contenders, it's more that he's proven he doesn't stop teams from becoming that.