For the record, I was a huge fan of having Johnson last season. As I stated he was one of my favorite pitchers in the MLB during his time with the Marlins, I felt he never got the recognition he deserved (ala Halladay). But, after what we witnessed last season, combined with his recent health issues over the last few seasons, it would feel irresponsible to put any kind of stock into him performing like his old self. If he was slotted as our number 2 pitcher heading into the season I would definitely be looking towards plans B and C before the season started.
With Ervin Santana, I wouldn't be expecting anything close to Johnson in his prime, but I would be able to confidently pencil him in as our #3 or #4 SP every day.
Maybe I just regurgitated what Jonn just said, but that's my 2 cents.