Harang as OD starter is not a given. When nobody on your staff is an ace, then it's wide open. I don't think you can just pencil Harang in. It'll be whoever's hot coming out of ST...could be Harang, could be anybody else.
Also it depends on how JN wants to set up the rotation. But I don't think anyone can assume it's going to start with Harang.
Also, I don't think the Reds are done making moves to try to bolster the starting rotation. Any move they make between now and OD will also be a factor.