“Do the Diamondbacks have the best rotation in baseball?” feels like a weird question to ask, not least because while there’s certainly a curvature to their movement, I’d call it more of a “slither” than a “rotation”…

But seriously, folks. It’s a legitimate question now.

For the first decade of their existence, the Diamondbacks were a team built on pitching. Randy Johnson and Curt Schilling, maybe the best one-two punch of the 21st century, led Arizona to a title in 2001, and even after that team broke up, Brandon Webb was the best pitcher in baseball for a couple of years. In 2008, Arizona went just 82–80, but with Webb, Dan Haren, and a 44-year-old Johnson (who posted a Satchel Paige–like 118 ERA+ in 184 IP), the rotation wasn’t the problem.

For most of this decade, that identity disappeared. Johnson retired, Webb blew out his shoulder, and Haren got traded to Anaheim in 2010. When the Diamondbacks last made the playoffs in 2011, the rotation featured a front four of Ian Kennedy, Daniel Hudson, Josh Collmenter, and Joe Saunders, all of whom pitched well that season, but weren’t exactly Maddux, Glavine, Smoltz, and Avery.

The Diamondbacks are currently in prime playoff position thanks to starting pitching the quality of which they haven’t had in years. It might be the best rotation in the game right now.

In recent years Arizona’s been more famous for the pitchers it’s failed to develop. In December 2009, the Diamondbacks jumped in on a three-way trade with the Tigers and Yankees that netted Kennedy and Edwin Jackson at the cost of former first-rounders Daniel Schlereth and Max Scherzer. In 2010, Arizona spent the no. 6 pick on Texas A&M right-hander Barret Loux, then failed to sign him after his physical revealed significant damage to his elbow and shoulder. The next year the team spent the no. 3 overall pick on Trevor Bauer, then jettisoned him 18 months later in another three-team trade after he clashed with coaches. One of the big jewels of the Haren trade, Tyler Skaggs, went back to the Angels in still another three-team blockbuster in 2013. That deal, which also cost the Diamondbacks Adam Eaton, brought back Mark Trumbo, who moved on to Seattle after a year and a half of replacement-level production. Athletic high school right-hander Touki Toussaint fell to Arizona at no. 16 in 2014; he lasted just 12 months in the organization before he was traded to Atlanta in a salary dump.

Even last season, the Diamondbacks invested heavily in pitching, and to say it didn’t work would be a gross understatement. They sent former no. 1 overall pick Dansby Swanson, pitching prospect Aaron Blair, and center fielder Ender Inciarte to Atlanta for Shelby Miller, who posted a 6.15 ERA last year and is now on the DL recovering from a torn UCL. Zack Greinke signed a $200 million-plus contract and made only 26 league-average-ish starters in his first year in Arizona. Robbie Ray, who cost starting shortstop Didi Gregorius in yet another three-team trade, posted a 90 ERA+ in 174.1 innings.

Along the way, Chase Field turned from a neutral park when it opened in 1998 to one of the most hitter-friendly stadiums in baseball. It was the second-highest run-scoring environment in baseball in 2014, and again in 2016 and so far in 2017.

Meanwhile, one thing Arizona has done well is develop position players. David Peralta, plucked out of indy ball, has a career 116 OPS+ now. A.J. Pollock never made a top-100 prospect list but produced a seven-win season in 2015. Inciarte and international free agent Gerardo Parra became superb defensive outfielders. Jake Lamb, a sixth-round pick out of Washington, is slugging .516 since the start of 2016, and you might have heard of Paul Goldschmidt, who was once an anonymous eighth-round pick out of Texas State.

You’d think, therefore, that if Arizona were capable of a season like this — with a 6.5-game cushion in the wild card at the break, along with the third-best run differential in the National League — it’d be on the strength of those position players. But while Goldschmidt, Peralta, and Lamb have all played very well, that hasn’t really been the case.

According to Baseball-Reference’s wins above average, the Diamondbacks have the best starting rotation by a win and a half over second-place Washington. FanGraphs has them at 11.2 WAR, six-tenths of a win behind the first-place Dodgers, but by ERA-, Diamondbacks starters are in first place. Arizona’s fifth in starter K%, though the gap from second to sixth is half a percentage point.

Each of those leaderboards contains an odd outlier or two, but if you look at them together, a group of five teams keeps ending up near the top: Cleveland, Washington, Arizona, Boston, and the Dodgers.

Cleveland leads the majors in starter strikeout rate at 26.9 percent, but ranks just 13th in ERA-, with a pedestrian 99. (This probably says more about the evolution of baseball than anything else, but Nolan Ryan and Sandy Koufax had career strikeout rates of 25.3 percent and 25.2 percent, respectively.) Cleveland shows up higher on FanGraphs leaderboards, however, because it’s underpitching its FIP by more than half a run — only the Giants are doing worse by ERA-FIP.

But Cleveland isn’t having a great season so much as Corey Kluber and Carlos Carrasco are having great seasons. Carrasco and Kluber are both in the top 10 among AL pitchers in bWAR, and Mike Clevinger somehow has a 158 ERA+ in 60 innings, but after that it gets ugly, which should come as no surprise to anyone who watched Kluber and a bunch of relief pitchers take this club to Game 7 of the World Series last season. Josh Tomlin, Trevor Bauer, and Danny Salazar all have ERAs above 5.00.

One or two great pitchers don’t make a great rotation. For that, you have to go four or five deep, and Cleveland doesn’t do that.

Neither does Washington, now that Tanner Roark’s ERA is 4.98 and Joe Ross is out for the season. Gio Gonzalez is second in WAA among all MLB pitchers, and is having the best season of his career, while Stephen Strasburg’s quietly striking out 10.2 batters per nine innings. Scherzer’s having one of the best pitching seasons of the past decade, and he’s been so good over so many innings that you could almost count him as two pitchers. Almost. It’s a very good rotation, but not deep enough to be the best in baseball.

Boston, however, has a deeper rotation than you’d think now that Eduardo Rodriguez (129 ERA+) and David Price (134 ERA+) are healthy. Chris Sale’s been by far the best pitcher in the American League this season, and Drew Pomeranz (9.8 K/9, 121 ERA+) has just about equaled his All-Star campaign from last season. Even Rick Porcello, who spent the first half on a Cy Young hangover, still has a 99 ERA+, which is far from disastrous for a no. 4 or no. 5 starter.

The Dodgers also boast significant rotation depth. While last year they signed about a dozen pitchers and most of them were hurt all season, this year the Dodgers have been able to field at least five quality starters from their rotating cast. Most important among these is Clayton Kershaw, who missed 12 starts with a back injury in 2016 but went into the 2017 All-Star break having pitched more innings than anyone in baseball. But collectively Dodgers starters have a higher K% than any team except Cleveland and a lower ERA- than any team except Arizona. Part of that is the immense innings total Kershaw’s worked so far, but Brandon McCarthy’s having what might be the best season of his career, while lefty Alex Wood has an ERA half a run below Scherzer’s.

But deep as the Red Sox and Dodgers rotations are, Arizona’s is even more so. There are 29 starters this season with an ERA+ of 130 or better in at least 60 innings pitched. The Diamondbacks have five: Greinke, Ray, Godley, Taijuan Walker, and Randall Delgado (who’s not really a starter, with five starts this year against 24 relief appearances). Houston (Dallas Keuchel, Lance McCullers, Brad Peacock) is the only other team with more than two such pitchers. Arizona’s used eight different starting pitchers this year, and seven of them have at least a league-average ERA+. The exception, Braden Shipley, has thrown only 11.1 innings in 2017.

Now, it might seem like Arizona doesn’t have the kind of ace who scares teams come playoff time the way Scherzer, Sale, Kluber, and Kershaw do. After all, it doesn’t matter that Patrick Corbin — Arizona’s fifth-best starter this year by ERA+ — would outpitch Josh Tomlin, because those guys wouldn’t pitch in the World Series if everyone were healthy.

Except, that all depends on how much stock you put into Greinke’s down year in 2016, because right now, Greinke’s sixth among qualified starters in ERA- and seventh in strikeout rate, with a lower walk rate than Scherzer or Kluber. Greinke feels like he’s been around forever; he made his MLB debut in 2004, two years before Kluber, Sale, Scherzer, or Kershaw pitched professionally at any level, and won his Cy Young in 2009, when Kershaw and Scherzer first qualified for the ERA title, Kluber reached Double-A, and Sale was a sophomore at Florida Gulf Coast.

Even so, Greinke isn’t exactly Old Hoss Radbourn. He’s only nine months older than Scherzer, and he’s two seasons removed from posting a 1.66 ERA in 222.2 innings, an effort that would’ve won him a second Cy Young if Jake Arrieta hadn’t posted an 0.75 ERA and thrown a no-hitter on national TV after the All-Star break. (Kershaw struck out 301 batters that year and finished a distant third.)

Plus, as far as no. 2 starters go, there aren’t many better right now than Ray, who’s striking out a higher percentage of batters faced than any qualified starters outside of Sale, Scherzer, and Kluber. He’s walking 11.9 percent of batters, fourth-highest among 70 qualified starters, but for comparison: Gonzalez is sixth on that list with a strikeout rate about two-thirds as high as Ray’s. In other words, right now Greinke and Ray could at least hold their own against any one-two combination in baseball.

On some level, the Diamondbacks do just feel a bit fluky. And it’s right to be a little suspicious, particularly of unfamiliar names like Ray and Godley, who have pitched like down-ballot Cy Young candidates over half a season after barely pitching like big leaguers in 2016. Last year, Greinke looked like he was in decline, well on his way to becoming Zack Greinke’s Contract. Walker was mediocre, far enough removed from his former top-10 global prospect status to be included in a “my garbage for your trash” trade between Arizona and Seattle. Godley, Ray, and Corbin were just flat-out bad.

But not all of that feeling is justified. With a new coaching staff and front office this season, the Diamondbacks are shaking off the bad reputation their baseball ops department earned in years past, and when you look at Greinke and Corbin’s past performances, Walker’s prospect hype, and Ray’s relative youth and high strikeout numbers, the only 2017 performance that looks shocking is Godley’s.

Even then, Godley’s DRA (2.74) suggests that he isn’t just getting by on batted-ball and clustering luck, and here’s how his underlying numbers stack up against those of other top ground-ball pitchers this year.

There isn’t a compelling statistical case that the Diamondbacks haven’t had the best starting rotation in baseball this year. You can argue that a more top-heavy group might fare better in the playoffs, or that Ray or Godley might falter down the stretch, or that having more familiar names in the back half of the top five is just more comforting. But no matter how you look at it, the Diamondbacks are probably headed back to the playoffs, and they’re doing so on the strength of outstanding starting pitching. It’s been a very long time since we’ve been able to say that.