That doesn't change the fact that Gotham City is still screwed, because there's no Batman. Sure, Bruce left all his gadgets and stuff to Blake, but that was an incredibly naive thing to do, because it ignores the fact that Batman's true superpower was always money. If his tank broke down or exploded, he just got a new one. Actually, forget the tank: What's Blake gonna do when something tears up his Batsuit, like the dogs at the beginning of The Dark Knight? Patch it up with duct tape?
Blake after two nights.
And that's the other thing: Bruce trained to be Batman by traveling the world for seven years, most of which was spent with a group of highly skilled assassins in the mountains. Contrast that with Blake/Robin, who was at one point overpowered by Gary Oldman in a hospital gown. What's going to happen when the Joker comes back (presumably he escaped from prison with the other criminals), or when a guy who looks like the Penguin as played by Philip Seymour Hoffman inevitably shows up?