Overall, he had solid numbers throughout his minor league career until 2013 AAA, then so many people lost faith in him.
IIRC, Mez had a bad year (or two) in his minor league career too.
Oh yea, and Lorenzen had a bad fall season and many gave up on him too. Now, Lorenzen is pitching well.
I don't know the story about Stephenson, but we can't read too much into minor league stats. Maybe the Reds have him working on something.
For example, just think how much better off Cingrani would've been if he was forced to throw more offspeed stuff in the minors, instead of 90% FBs.. maybe he would be doing less "learning on the job" in the majors. I'm not worried about Stephenson having a bad year in AA.