When your rushing attack is so impotent that it only takes 4-5 committed defenders to stop it, the RO is useless.
This leaves two defenders free. They can use an end, linebacker, or safety to seal the edge and another to close the C gap. As long as these guys let the play come to them, and don't overpursue, it won't matter where the ball goes.
The RO works well when you have a dominant rushing attack and the defense has to stack the box, and focus on the runner, leaving only one defender free to cover the C gap and seal the edge. It can also work when you have a defense that doesn't play disciplined, and overpursues the play. If you can draw the C gap guy into the backfield, it reopens the gap for an attack. A defense can attack the mesh point, but it's risky. Better to let the play develop and attack after the decision is made.
RO can also work if you don't have a "running QB" and you can sucker the defense into ignoring the QB, but you can't do that very often anymore.
Defenses are getting better at playing disciplined against the RO. Maintain gap control, let the play come to you. Patience is the key to shutting it down.