Chapman was always a starter his entire career before being converted to a reliever and last year, a closer. Some people posting seems to think this is foreign territory for him.
We aren't paying 7 mil a year to Broxton to set up.
This shouldn't even be a discussion at this point. Stick with moving Chapman to the rotation and if things don't look good in June/July, move him back to the bullpen for the remainder of the year and do it over again next year.
Relievers are a heck of a lot easier to find than plus starters.