Protrade gives their prediction on Josh Johson's future.
His drop off after the All-Star break doesn't concern me so much. Josh's ERA and BAA started to increase in September when he throwing more innings than he ever had before. This is not uncommon. The other thing is who knows when his forearm started hurting. Maybe it starting turning before his final start of the season. Only Josh really knows.
I tend to agree with their statement that he will end up being a solid middle of the rotation starter - not an ace, on the Marlins rotation anyway. I'm not exactly sure why I think this, or at least, I can't articulate it at the moment. But the only way to know for certain is to trot him out to the mound, next season, and see what he can do.