After Jordan Montgomery signing, do Diamondbacks have MLB's best pitching rotation?

For all the good work the Arizona Diamondbacks did this off-season, ballooning their payroll to unprecedented heights and filling every need on the roster, their starting rotation was never expected to be among the very best in baseball.

When Fangraphs unveiled its projections over the winter, the Diamondbacks’ rotation slotted in as the 12th most valuable. Over the following months, it generally inhabited that space. Even Zac Gallen, the ace of that rotation and the starter Thursday on Opening Day, labeled it “probably fringe top seven.”

Now?

“Top three, I think, easily,” Gallen said. “There's some good arms in our division especially but just the depth that we have, proven track record of guys that I think you'd be hard-pressed to put us outside the top three.”

The difference, of course, came Tuesday, when the Diamondbacks signed free-agent left-hander Jordan Montgomery to a one-year, $25 million contract in a stunning deal. Montgomery has been one of the sport’s most reliable starters over the past three seasons, making 30 starts in each of those years and posting a cumulative 3.48 ERA. For much of the off-season, Montgomery had been expected to receive a nine-figure contract until he — like fellow Scott Boras client Blake Snell — went unsigned and had to settle for a short-term deal.

Now, the Diamondbacks' rotation has a rare combination of aces and depth. Zac Gallen and Merrill Kelly remain one of the better 1-2 punches in baseball. Montgomery, once he ramps up his workload, will slot in somewhere in that mix. Eduardo Rodriguez is a middle-of-the-order arm even if he might technically be the Diamondbacks’ No. 4 starter. That leaves Brandon Pfaadt, a postseason hero last fall, as the last member of the rotation, with Ryne Nelson and Tommy Henry on the outside looking in.

All of it begs an incredible question: Is the Diamondbacks rotation the best in baseball?

After the Montgomery signing — which is still unofficial pending a physical — Fangraphs projects the Diamondbacks to have the fourth-best rotation, by total WAR. Only the Dodgers, Phillies and Braves rank higher.

There is even some reason to believe that those projections underestimate the Diamondbacks.

The gap between the Diamondbacks and the top three teams is a product of the top of their rotation, not the bottom. Rodriguez is projected as the sport’s most valuable No. 4 starter, with Pfaadt as the most valuable No. 5 starter. Gallen, Montgomery and Kelly, meanwhile, do not grade out as well as many would expect. Among all starters, Fangraphs projects them to rank 17th, 24th and 44th, respectively.

Those three pitchers, though, were all among the top 16 qualified starters in ERA last year. Together, they combined for 12.7 WAR — more than the top three pitchers on any other team.

Put it all together and the Diamondbacks’ rotation consists of five starters who posted a 3.60 ERA in 825 innings. On one team, that would have amounted to the best rotation ERA in baseball.

“We've got some dudes going out there every couple days,” Christian Walker said. “I think our staff was great already and we added another awesome piece to it.”

Walker’s enthusiasm was a common sentiment in the Diamondbacks’ clubhouse Wednesday. “It shows how much (the front office) believes in us and I think that plays a big role,” Joc Pederson said. “When you know the front office, the ownership believes in you guys and are gonna give you everything you need to win, it's gonna be a fun year.”

Gallen echoed the importance of that vote of confidence.

“Arizona's not a team that tends to spend a lot of money,” Gallen said. “There's been contracts here and there but never all at once, it seems. So for ownership, management to (show) ‘Hey, if you give us a team to invest in, we'll invest in it.’ And then we go out and do our job and then on the flip side, they went out and held up their end of the bargain.”

To Gallen, that support showed that management shared the players' desires to improve the roster.

“That weighs a lot, especially inside of the clubhouse,” Gallen said. “… A lot of guys were pretty fired up about it.”

This article originally appeared on Arizona Republic: After Montgomery signing, do Diamondbacks have MLB's best rotation?