Well, if you traded for Chapman as a reliever, you could convert him into a starter anyway, lol
Assuming Chapman is like a 4 win pitcher (JFaS posted numbers I think?), you'd be paying 5 cheap-ish years of a 2.5-3 win pitcher for 1 year of 4 wins at a not-inexpensive salary and then maybe the right to pay him at the very least market value