Josh Collmenter completely belongs as the long reliever.
Josh Collmenter needs to become a starter right now.
Is there any chance both of those two statements are true?
I have a theory into Josh Collmenter's success. Hitters simply aren't prepared for Josh Collmenter. When Josh is a starting pitcher, hitters can watch a lot of video to prepare for his start. They can learn to time out their swing and pick up the ball in that funky delivery. The hitting coach can go over the game plan with each hitter based on scouting reports and pitch tendencies.
Most hitters prepare for the starting pitcher and the closer. Situational guys prepare for the reliever they think they'll face late in the game. No one prepares for the long reliever. Collmenter's stuff is not that overwhelming. Collmenter's delivery isn't either if you have four hours to get ready for it. Even a professional hitter is going to struggle against Collmenter if they spent all day preparing for Cahill and get six innings of Collmenter. Managers stack their lineup to face one type of pitcher only to get hit with something completely different so they struggle with matchups the rest of the game.
A manager's job is to put his players in the best situation to succeed. Collmenter in long relief is what's best for him in the long-term. However, for the D-backs, there won't be a long-term if the short term isn't handled properly. Depending on Cahill's condition, three-fifths of the rotation will miss a turn. Unless Archie Bradley, Tyler Skaggs and Randall Delgado are all to become fixtures for the month, it's time for Collmenter to start.
I want Josh Collmenter to be fixture in the D-backs' bullpen for years. I think he will pitch in the Majors for over 10 years and have a great career as a reliever. I don't even say "long relief/spot start." He's not at his best as a spot starter. The term "spot starter" means one pitcher will miss one turn in the rotation for any number of reasons and you need one other guy to fill in his spot. This is not the situation the D-backs are in. There are multiple holes in the rotation due to McCarthy's injury, Kennedy's suspension and the pending diagnosis for Trevor Cahill.
If Cahill goes on the DL, Collmenter should start. This division has four teams at or above .500 and no one is pulling away. Every game could be the difference in a division that will go to the wire. Having Collmenter in long relief is a luxury for both him and the team that neither can afford right now.