Is it going to help?
It's doubtful whether the signing of Arroyo, in a vacuum, will move the needle very much for the 2014 Diamondbacks. Taking an average of the Steamer and Oliver projections from Fangraphs.com, for the three pitchers who are the main contenders for the fifth spot in our rotation - with the potentially slightly wobbly assumption Miley, Corbin, Cahill and McCarthy are locks - here's what we find [Note, the numbers for Arroyo are pre-move, and so reflect him pitching in the Little American Ball Park, rather than at Chase Field. Bradley is Oliver only, since Steamer has him projected to throw a whole one inning!].
Obviously, these are projections, so should certainly not be treated as gospel. But it doesn't seem to suggest that Arroyo will be significantly better than the other two possibilities in the 2014 rotation. He certainly isn't the top of the rotation starter Kevin Towers was looking for going in to this winter. By any measure other than the dreaded WINZ, the last time Arroyo was a particularly good pitcher was probably 2006, with an ERA higher than 3.70 ever year since. League average for a starter in 2013 was 3.86, and Arroyo has been within a dozen clicks of that in four out of the past five campaigns. Consistently mediocre, in the best sense, seems a good way to describe his recent performances.
As we noted previously, no pitchers has made more starts than Arroyo over the past ten years: he has been the most reliable of reliable things. In a where where Kevin Towers considers three years the top end of pitching contracts, due to their potential risk, the last time Bronson missed a start was when he was used out of the bullpen a couple of times by the Red Sox, in May 2004. Part of me thinks that makes him a certainty for 200 innings this year. Part of me thinks he is overdue to come up snake-eyes on the craps table of health. But the fact he is a soft-tosser might help, since he hardly puts more stress on his arm than R.A. Dickey
For by "soft-tosser", I mean of the 81 qualifying pitchers last year, his fast-ball was ranked 78th in velocity. And he used even that not-so-fastball, less often than Mark Buerhle and Eric Stults, two of the three below Arroyo (Dickey being the third). His secondary pitchers are even slower: contrast Buerhle, say, who also throws a cutter about a quarter of the time, in the low 80's. The bulk of Bronson's arsenal in 2013 - 55.6%, to be precise - consisted of a slider (average speed 75 mph), a curve-ball (71.9 mph) and a change-up (positively rushed up there at 77.5 mph). You don't need a radar gun to monitor Arroyo; a calendar will do just fine.
It's worth remembering, as ever, that teams almost always need more than five starters over the course of a season. Last year, our five most regular rotation members combined for 133 starts, so that was 29 - almost another entire starting pitcher - left to be accounted for. It would seem sensible to plan for something similar, with Brandon McCarthy the most likely candidate, going by past experience. The signing of Arroyo means that, rather than having to bring Bradley up, or promote a replacement level pitcher from Reno, we can use Delgado as the "sixth man". We don't know when that might be, or for how long, but it's almost certain it will be necessary at some point.
Growing old disgracefully
Oddly, Steamer takes a dim view of Arroyo's stamina, having him pegged for less than 100 innings. This seems odd, since he hasn't thrown less than 199 innings for a decade: It's likely a function of Arroyo's age, and you can understand why, as pitchers at this point in their career appear to become increasingly fragile. Over the sixteen seasons since the D-backs came into the league, here are the number of pitchers at each age Arroyo will be during the potential life of this contract, who have simply qualified for the ERA title i.e. reached 162 innings. Links go to the list of pitchers, so you can see who they were and how they performed. You're welcome!
Not many. As Satchel Paige put it, "Don't look back. Something might be gaining on you." That said, those veteran pitchers performed rather well, with a median fWAR of 3.5 at age 37, dropping to 2.9 at age 38, then actually increasing to 4.4 WAR for 39-year-olds. However, there's an undeniable self-selection bias involved here, since if you get to pitch 162 innings in the majors at that age, it's probably because you were pretty good up to that point. As noted above, the last time Arroyo had a 3.5 fWAR season was in 2006, so expecting him suddenly to pull one out of his, ahem, leg-kick now is probably unrealistic. And as shoe pointed out, non-strikeout pitchers seem to age worse than usual.
The focus is, naturally, on where this will leave the team for 2014. But it's perhaps worth looking at what might happen for the two years beyond that where Arroyo is under team control This is Brandon McCarthy's last year as a current Diamondbacks, but I would imagine Bradley should be ready for a full-time role next season, giving us a probable rotation of Arroyo, Bradley, Trevor Cahill, Patrick Corbin, Wade Miley. As well as the $11 million option on Arroyo for 2016, we have a $13 million team option on Cahill, so that could be the way we line up then as well, but Braden Shipley could be knocking on the door to displace one of them by that point.
Arroyo seems to me to be an expensive insurance policy, albeit one covering us for a need that is almost certain to be required in 2014. On that basic, I think there is a case that he does make the team "better", because his presence will help us avoid the need to burn a year of Bradley, or dig into the replacement-level or thereabout pile of starters. But at $9.5 million, it doesn't feel like great value, and the $4m option for 2016 is definitely too high. Of course, by then, the team should be rolling in a new TV contract and that'll be relative pocket change. But I suspect this one won't turn out to be very good overall value for the Diamondbacks.