I think some might be ignoring the effects of moving a guy from the rotation in the spring, to a relief role in the bigs leagues, then back to the rotation in April, May or June. Then if someone gets healthy he'd go back to the bullpen and do it all again. I guess that's what swingmen do and I can't say with any certainty that it has an adverse affect either so perhaps it is the right move.
I don't find the argument regarding "downgrading the big league team" to be all the persuasive though. We are talking a handful of innings in a middle relief role over the course of the first couple months of the season. Those innings are probably made up when he can come in and pitch 6 to 7 innings unrestricted instead of 3 innings one start, 4 the next, then eventually he's got no restrictions. And of course, they may send him down to the bigs to stretch out while a shitbag like Rowley gets the interim starts anyway. This FO has done that before. The #6 SP is a key member of the big league team anyway. It's a more important position than a middle relief role IMO.