Scouting reports have never been that favorable to Johnson's stuff. He can throw hard but its relatively straight..mediocre secondary pitches.I think I've seen enough of Hunter to determine that he's at best a #4 type and most likely a 5th. And as you said, better used in the 'pen. Ideally I think he's your long reliever.
I need to see more of Johnson, but I could see him getting lit up if he performs like he did in his debut.
I mean, you never know..maybe he learns a new pitch or something like that. Also, he could certainly be capable of getting hot down the stretch here and making 5-7 good starts. I think most players at the ML level are capable of being really good for a short stretch of time...they are afterall, professionals and the best at what they do in the world.