I don't see him any better than a 4 a big MAYBE that he develops into a 3.
It's much too early to judge Detwiler. THis time last year, he looked like a complete bust. Then, he found his equalibrium and began to have a bit of success, but too soon he was pressed into service at a level way above his previous experience. He needs to go back down, but I expect him to come back next season as a solid middle rotation guy. Yeah, 3-4 is likely, but I wouldn't foreclose the possibility of #2. Small chance, but a chance.