Here are the pitchers that have started for the D-backs this season, with their run support.
Wade Miley: 4.5 runs per start (but this includes three starts with double digit run support, take those away and it drops to 3.15. He receives 5 or more runs of support less than one-third of the time.)
Patrick Corbin: 5.07 per start (the D-backs have scored between 2 and 9 runs in every Corbin start. He's received 5 or more runs of support in 8 of 15 starts.)
Ian Kennedy: 4.57 per start (one start with 12 runs in support, but fairly consistent. He's gotten 5 or more runs of support in 6 of 14 starts.)
Trevor Cahill: 3.25 runs per start (and this includes 2 starts with 9 runs. Take those away, and it drops to an astounding 2.42. SEVEN times Cahill has received only 1 run in support. He receives 5 or more runs in support less than one-third of the time. He and Miley both have received that level of support in 5 of 16 starts.)
Brandon McCarthy: 4.45 runs per start (one start with 10 runs, but fairly consistent. Seven of his 11 starts had five or more runs in support, easily the highest percentage on the team.)
Skaggs/Delgado (figured together to increase the sample size): 3.8 runs per start.
What does this mean? Patrick Corbin has not only been our most consistent starter, but has received the highest and most consistent run support. Wade Miley has received the most inconsistent run support; three offensive explosions, but outside those, a measly 3.15 is the worst on the team. He and Cahill have certainly been hindered by a poor offense.
I believe that when your pitcher gives you a quality start, you should win, and that when your team scores five or more runs, you should win. The Diamondbacks are 25-8 when scoring 5 or more runs, which is acceptable. But quality starts have not translated to wins as often. Here are the quality start figures, with the team's record in those games:
Patrick Corbin: 13 QS, 12-1
Wade Miley: 10 QS, 5-5
Ian Kennedy: 7 QS, 3-4
Trevor Cahill: 6 QS, 4-2
Brandon McCarthy: 4 QS, 3-1
Tyler Skaggs: 1 QS, 1-0
Randell Delgado: 1 QS, 0-1
Overall, that's a 28-14 record when we get a quality start. While the QS statistic should be tweaked a bit (runs should be the determining factor, not only earned runs) the fact that we have won only two-thirds of the time our starters have given us a great chance to win isn't good.
55% of the time, our starters give the team a good chance to win. 43% of the time, the offense scores 5 or more. Thus, I'd put the blame for us only being 3 games up on the rest of the division on the offense, not on the pitching, even taking the bullpen into consideration. A lot of people on here want to blame Cahill (who hasn't been very good this month, admittedly) and Miley, but they just aren't getting the run support. In the last month, Corbin hasn't been getting the run support either, and thus hasn't been able to notch that 10th win. Hopefully, the return of Hill and Chavez will provide a spark to the offense. Hopefully Prado is heating up as well (he's gotten on base in seven of the last eight, and has demonstrated more patience at the plate.) With Parra, a healthy Hill, Goldschmidt, and some improvement to be expected from Montero, Ross/Kubel, and Prado, this team should only get better. Hopefully, they can not only stay on top of the division, but pass the Braves for the number 2 seed in the playoffs (don't know about everybody else, but I'd rather face the wild-card than whoever wins the Central.)