The Reds aren't the team that skips guys over levels like that. At least not guys like this. College guys going from rookie to High A, sure. But Stephenson isn't going to go from Billings at 19 to High A at 20. He isn't going to go from High A at 21 to AAA at 22. He is a guy who is going to hit every level on the way up from wherever he makes his first start at. If they start him in Billings, he will be in Dayton next year because there won't be enough time for him to do enough of both Billings and Dayton in 2012 for him to start in High A in 2013.
As far as what happened with Sulbaran.... I think his situation is different from the others. He was clearly not mature enough his first time through Dayton. As you noted, he didn't take his work seriously. There were reasons for that, which I won't go into and he has gotten beyond that. The other guys all didn't seem to have that problem. If the Reds were going to change their philosophy because of Sulbaran, they wouldn't have had Jacob Johnson in Dayton when they did. Sure, he had some experience as a pro. In the Gulf Coast League, with no one watching but the players and coaches. Stephenson probably starts the year in extended spring training, but I would say the odds that he makes it to Billings are less than 20%. Maybe I am completely misreading things here, but the Reds haven't been shy about promoting their premiere guys at all. Stephenson is exactly that type of guy.