We're paying him $12 million regardless
The team is on record that money played no part in the decision. Said Chip Hale: "The coaching staff and the front office had talked about it and they made it clear: You guys do what you need, take the five guys you want to start with and we’ll deal with the rest of it". Because what is the alternative, in terms of public announcements? "Yeah, we've got better pitchers, he's only on the roster until some other team gets desperate enough to take him off our hands. We're hoping for a particularly fluky April BABIP to enhance the illusion." So, I put no faith in this statement. Indeed, I hope money did play a part, since if not that would demonstrate a worrying degree of profligacy.
He is a sunk cost. We can flush the money down the drain, release him - then watch some other team in the division pick up our discard, before Cahill comes back to throw a near-perfecto against us. I didn't enjoy that movie the first time I saw it, and would rather not endure a remake. Or we can hang on to him, and see if he can raise his value from the current near-zero. For make no mistake, that's where it is: nobody wants a pitcher earning that much, coming off a season where they went 3-12 with a 5.61 ERA, were demoted to the bullpen and accepted a voluntary assignment to the minors. If there had been any meaningful offers, we'd have taken them.
Cahill could still turn it around
2015 was utterly rancid, but in both his first two years for the team, he posted a sub-four ERA, and over that pair of seasons was worth between three and four wins above replacement, depending on your metric of choice. Certainly, the trend has been down, for quite some time. But he's still young. In fact, Cahill is younger than Chase Anderson or Vidal Nuno, and in our Opening Day rotation, only Rubby de la Rosa will be younger. And Cahill's FIP - generally regarded as a better predictor of future performance - was 3.89, basically indistinguishable from Collmenter's 3.89, mostly due to Cahill's K-rate, a career high. Let's play the old "Pitcher A/B game", with a pair of sinkerballers:
Which one would you reckon had the better future? No surprise to learn that Pitcher A is Trevor Cahill in 2014. Pitcher B was Brandon Webb in 2004. The next few seasons worked out fairly well for him and the Diamondbacks, as I recall. Now, this is obviously far from a sure thing. But as Wayne Gretzky once said, "You miss 100% of the shots you don't take." I would say there's probably about a one in four chance of him getting to the point where we can trade his contract without having to throw in a prospect to sweeten the deal a.k.a. Heath Belling him. And a slim (maybe 5%?) chance he's so completely fixed we can think about those 2016 and 2017 options. That'd be nice.
Certainly, he has had a better spring this time around. The numbers aren't entirely comparable, because Cahill has had some B-game appearances this pre-season, but after today's outing, here are the comparable figures:
2014: 6.95 ERA 22 IP, 34 H, 18 R, 17 ER, 4 HR, 6 BB, 22 K
2015: 3.60 ERA, 10 IP, 14 H, 4 R, 4 ER, 0 HR, 4 BB, 10 K
The strikeout rate is identical, and the K-rate similar, but Cahill has done a much better job of keeping the ball in the park this spring. He is getting a lot more ground-balls as well, about double the rate of last spring. While you must insert the usual disclaimers about small sample size, etc. there does appear to be some grounds for hope.
The alternative options
There is certainly a credible case that putting Archie Bradley in the rotation from Opening Day, would give the team a better chance to win in 2015 than Trevor Cahill. However, other things being equal, doing so would cost the team a year, with our years of control then covering 2015-2020. Waiting even a few weeks now, would mean Bradley is still under the six years necessary for free-agency at the end of 2020, so retaining Arizona his services for 2021. And which would you rather have? His rookie campaign, his age 22 season, in a year where we're unlikely to compete, or his age 29 season, when we will likely be in a much better situation?
Again, Dave Stewart has publicly made it clear that service time is not a consideration. However, the same goes here as for the salary situation: if player control is not a factor, I would want to know why., because it should be something the team thinks about. However, downplaying it makes a lot of sense, both in the light of the current kerfuffle over another top prospect being sent to the minors, the Cubs' Kris Bryant (with the players' union threatening to file a grievance), and the comments of Bradley's agent, Jay Franklin, last spring. After Archie was sent down, Franklin said, "I think it's very apparent what is going on in Arizona."
The above applies equally as much to other top prospects, such as Aaron Blair. Beyond them, it's hard to come up with many where you can make a clear case they would represent a palpable improvement over Cahill e.g. Robbie Ray, Allen Webster. Daniel Hudson has pitched well, but that limited pitch-count is a big red flag for me, as far as starting. The one for whom you could make the best case, might be Randall Delgado. However, we've seen the value of a good long-man before (Josh Collmenter in 2013: 1.74 ERA over 62 IP, when working 2+ innings), and given our rotation, Delgado may be more useful throwing two or three innings a couple of times a week.
It's only Opening Day
Worth bearing in mind what happened to our Opening Day rotation last year. Cahill and Delgado were moved to the bullpen by mid-April due to ineffectiveness, Bronson Arroyo blew out his elbow against the Nationals in mid-May, and Brandon McCarthy was traded to the Yankees. By the last turn through before the All-Star break in mid-July, Wade Miley was the only rotational survivor for the Diamondbacks, with the other starts being from Collmenter, Anderson, Nuno and Mike Bolsinger. This is not a lifetime commitment. Cahill didn't last a month last year, and that was with the front-office who brought him here, and presumably had every incentive to stick with him.
So, as far as I'm concerned, it's almost all upside. Worst-case scenario: Cahill sucks and is disposed of after April, with one of the alternates then getting their chance. I am sticking my neck out here, but I doubt one month of Cahill will be a difference-maker for the playoff hopes of the 2015 Diamondbacks. Best-case scenario? He returns to 2013 form or better, giving us a solid member of the rotation, and Dave Stewart has to decide whether to trade or keep him, perhaps depending on how the season overall is going. I think having him in the rotation is the right move, albeit one aimed more at making the most of a bad situation inherited from the previous regime.