The truth is, no one knows what the D-backs starting rotation will look like when the season starts. I've seen a lot of different projections, and I have no reason to assume one over another. But I wanted to look at what might be, and compare that with teams that I remember contending (preferably winning it all) over the past 25 years or so to see what the similarities were. For this exercise, I'm looking at a rotation of Collmenter-Anderson-Nuno-Cahill/Arroyo-Ray/Corbin (split because Corbin is due back in June and if Cahill is underperforming he'll likely be replaced by Arroyo at some point.) A rundown of what can be expected?

Collmenter is vastly underrated, in my opinion. Yes, he doesn't have stuff that jumps out at you. But it's hard to argue with the results. In four seasons (two in the rotation and two in the bullpen, primarily) he's never posted and ERA or FIP over 4. Thanks to his control, he's never had a WHIP over 1.26, which came in his worst season, 2012. While he strikes out a lot more people out of the bullpen, he's effective either way. He's been worth 6.5 bWAR over 4 seasons, and never had a negative value. Sure, the league might figure him out, but after his performance last season, that is looking less and less likely. His struggles had always come the second and third times through the order, but last year he actually performed better the second and third time through. His projections released so far project him to have the worst season of his career, and while it might happen, I don't see it happening. I think he'll have another unremarkable season with an ERA in the mid 3s.

There's not nearly as much data on Anderson. He got a RoY vote last year, but was frequently the beneficiary of great run support. He posted an ERA of 4.01, slightly outperforming his FIP (4.22) and posting a value just above replacement level (0.9 bWAR). If he simply repeats that performance he'll be a key, but unremarkable, part of the rotation.

Vidal Nuno is a pitcher who looks like he should be terrible in Chase. He gives up a lot of fly balls, which is generally a bad sign, but can be made to work (see Collmenter, who has almost a 2:1 FB:GB ratio for his career but has been very successful at Chase.) After coming over from New York, his hits and walks dropped, and his strikeouts increased. That would be expected, but it was a bit more so than the expected transition from AL to NL. It was also more in line with his career minor league numbers. He's not going to set the world on fire, but he should be a solid #3.

Trevor Cahill is the opposite of most of the rotation. He has the stuff to be very successful, even a contender for Cy Young awards. But he's been inconsistent, and mostly dismal since arriving in the desert. If he returns to the form he had in 2010 or 2012, he could be the TOR arm the D-backs need. Or, assuming the D-backs are out of contention, he might fetch a return on the open market. If he struggles as he has the last two years, he will probably be designated for assignment when Bronson Arroyo returns. If Arroyo makes it back in his normal form, we know what we have: a solid but unspectacular starter who is a #3-4.

Robbie Ray is another wild card, and he might well not occupy this spot. He's young and has little experience at the MLB level. He could turn into another one in the line of Collmenter/Miley/Corbin (although he has better stuff, when on, than this trio) or he could be a failure. We'll be counting on the former. When (and if) Corbin makes it back, we'll hope he still has the form he showed in 2013, but there's really no way of knowing. The good news is there are plenty of pitchers to occupy the #5 spot, and one of them is bound to be replacement level.

Now, what of other rotations of contending teams over the last few decades? I'd hazard that the rotation above can be worth up to 10 bWAR, and don't figure that any single member will be worth 5. Have there been any World Series teams that reached the World Series despite that? Believe it or not, since the late 80s there have been 11, and 5 of them went on to win the series. More shockingly, 6 of them are post Mitchell Report, which fits in with my theory I've stated before that offense is becoming more important in terms of winning championships, simply because pitching is now a commodity that everyone has.

Teams with less than 10 bWAR from the top five starters (in terms of appearances) and no starter with >5 bWAR:

The first team I thought of was the Giants in the late 80s. In 1988, they started the year with a rotation of Dave Dravecky-Kelly Downs-Mike Krukow-Mike LaCoss-Rick Reuschel. In earlier years, Atlee Hammaker was a key part of the rotation, and in 1989 when they won the pennant Don Robinson and Scott Garrelts played roles, along with spot starts from Krukow, Dravecky, Bob Knepper, and Terry Mulholland. There are some famous names on that rotation, but none of them are particularly famous for what they did on the baseball diamond. Dravecky is most famous for his struggle with cancer, which robbed him of most of his 1988 season and the rest of his career. Krukow is more famous for being an announcer. LaCoss was basically replacement level (1.1 bWAR) over a 14 year career. Reuschel was the ace of the staff, and he was in his late 30s and early 40s, but had a decent career, posting 68.2 bWAR over 19 seasons. In 1989, the five starters with the most starts amounted to 7.8 bWAR, with Garrelts top value at 4. Of course, they were swept by the A's, who had a much better rotation, as well as a great offense.

The 1993 Blue Jays' five most used starters accumulated 7.5 bWAR, topped by Juan Guzman and Pat Hentgen, both with 3.4. Jack Morris really let them down, with -1.5 bWAR. Several future D-backs were on that team, including the first D-back All Star, Devon White, and the Blue Jays won by offense. Future Hall of Famers on the team included Paul Molitor (the WS MVP), Roberto Alomar, and Rickey Henderson. John Olerud was at his peak, mashing .363. Safe to say, if the offense performs like this, the pitchers barely need to show up.

The 1997 Indians, despite having some good pitching in terms of the names (Orel Hershiser, Charles Nagy) were worth only 7.6 bWAR. Nagy's 3.7 led the rotation. The Marlins weren't great either, but Kevin Brown's 7 bWAR kept them off this list, and an even better season in San Diego the following year kept them off the list. That 14-11 Game 3 makes sense.

The 2002 Giants were worth 8.5 bWAR, and no pitcher over 3.

The 2004 Cardinals's top 5 starters were worth 8.9 bWAR. They were led by Chris Carpenter's 3.3

The 2007 Rockies are on here, of course, because pitching and Denver just don't go together. Shockingly, although their top five starters were only worth 8.8 bWAR, no one had a negative value.

The 2008 Phillies got only 5.3 bWAR out of their top five starters. Cole Hamels led the team with 4.3.

The 2010 Rangers weren't very good on the mound. Their opening day starter, Scott Feldman, was worth -1.2 bWAR. C.J. Wilson led the rotation with 4.4. The top 5 were worth 8.5.

The 2011 Cardinals got only 6.5 bWAR from their top five starters, led by Chris Carpenter with 3.5

The 2012 Giants make the list, with 6.5 bWAR from their top five, led by Matt Cain with 3.9.

And the 2014 Giants round out the list, even if Jake Peavy (the sixth starter in terms of appearances) is added. Without him, they were worth 6.1 bWAR, and with him, they were worth 8.2.

(Dis)honorable mentions:

I thought the 1991 Twins might fit in here, but a career year by Kevin Tapani (6.8 bWAR) means they don't. But their preseason rotation, despite the presence of Jack Morris, didn't look very solid.

The 1992 Braves just missed the cut, as the 5 pitchers with the most starts were worth 13.2 bWAR, with no one worth more than Tom Glavine's 3.8. It's shocking for a team that was known for their great pitching, but they didn't perform as well in 1992 as they did in other years.

The 2006 Cardinals may have been the worst team ever to win the World Series. They missed the cut thanks to Chris Carpenter compiling 5.1 bWAR, but their top 5 starters were only worth 3.2 bWAR. Yes, the other four starters had a negative value. It would be hard for the D-backs rotation this year to be any worse.
What does this mean for the D-backs?
Not much, really. The fact is, even though these teams didn't have good pitching performances during the season, those that went on to win the World Series generally still had a bona fide ace that had underperformed during the season. It does show that with a good offense, it is entirely possible for the D-backs to compete. Still, it's highly unlikely that they could win it all until they find a top of the rotation arm to head up the rotation. But the team isn't as far away as we might think, and if everything develops as it should, and there is a little bit of luck, we could see the D-backs in the postseason, even in 2015.