This could be MLB's most underrated rotation

The Pirates were just 3 1/2 games out of the second National League Wild Card slot when they traded for Chris Archer at last summer's non-waiver Trade Deadline. Pittsburgh was doing its due diligence, giving up a pair of talented but unproven players in Austin Meadows and Tyler Glasnow to add a borderline ace for a postseason push.
Archer, as it turned out, was much the same pitcher with Pittsburgh as he was to begin the season with Tampa Bay -- which is to say, not a staff-leading ace -- and the Pirates fell short of October. But the club's growing rotation depth dictates that Archer doesn't have to be that traditional No. 1 over his next two seasons in western Pennsylvania. It's that reason why the Bucs might have baseball's most underrated starting unit heading into 2019.
There's the super rotations we already know about in the Indians, Astros, Yankees, Red Sox and Dodgers. Patrick Corbin replenishes the top of the Nationals' depth chart, and the Mets remain strong, given that their stars stay healthy. The Rockies' rotation could stake its own claim to "most underrated," but their starters got proper recognition last year for fueling the team's postseason run. Here a few reasons why the Pirates' starters are worth paying more attention to:

Jameson Taillon -- not Archer -- looks like an emerging ace
The expectations that surrounded Taillon when he was drafted nearly a decade ago are finally coming to some fruition. Taillon traded his sinker for his four-seamer as his primary fastball last year, which paired better with one of the better curveballs in the game, while also mixing in a new slider that paid off with good results. Taillon bumped his strikeout rate by nearly two points, and his whiff-per-swing rate by nearly four points from 2017 to '18, all the while maintaining his ability to suppress hard contact. In fact, only two full-time starters have allowed fewer barrels -- the most damaging contact a hitter can put in play -- per batted ball than Taillon since the start of '17.
Combining Taillon's burgeoning ability to miss bats with his contact suppression equaled a .285 expected weighted on-base average (xwOBA) -- Statcast™'s all-in-one metric, explained in more detail here -- which placed him 25th among starters who faced 500 hitters, in line with Charlie Morton and James Paxton. Taillon put together a 2.63 ERA over his last 21 starts once he fully introduced the slider, and there's plenty of evidence to suggest that he can maintain that level this season.
Trevor Williams and Joe Musgrove are showing promise
Those who poke around Baseball Savant's exit velocity leaderboards are probably familiar with Williams' name by now. The third-year righty has an old-school approach, throwing a fastball on nearly 70 percent of his deliveries, but he's made it work through superb contact suppression:
Williams' ranks among starters in 2018, minimum 300 balls in play

Hard-hit rate allowed: 30.6 percent (tied for 10th)
Average fly ball/line drive exit velocity: 90.6 mph (11th)
Slugging allowed on contact: .455 (7th)
Williams' four-seamer was particularly hard for batters to square up as last season progressed, as opponents hit just .174 against the pitch after the All-Star break -- a mark bested only by Walker Buehler, Rick Porcello and Blake Snell. Williams could certainly stand to miss more bats (his whiff rate was among MLB's worst), but two straight seasons of excellent contact metrics suggest that he's finding a way to be an effective mid-rotation starter without the punchouts.
Meanwhile, no starter in baseball pounded the strike zone more and threw fewer pitches per inning than Musgrove in his first season as a Pirate, cresting on Aug. 30 when he began an outing with a modern-record 21 straight strikes.

Flirting with the zone that much can be dangerous, but Musgrove's .280 xwOBA actually bested Taillon and Williams, though a right shoulder strain to begin the year and an abdominal surgery late kept him to 115 1/3 innings. His slider looks a solid putaway pitch moving forward, easing some of the sting of seeing Gerrit Cole flourish in his first season as an Astro.
Archer might be willing to tinker
Archer's declining numbers are no secret, and his fastball has been knocked as teams have grown accustomed to seeing his slider as his primary pitch. But perhaps change is afoot: Archer began mixing in some two-seamers and curveballs once he arrived in Pittsburgh, and told MLB.com's Adam Berry that he's willing to start changing up his offerings to make himself more unpredictable.
"I felt like when I was at my absolute best, I had that. And I got away from it," Archer said of his two-seamer. "I was getting more swing-and-miss, but there's times where you need contact, too. Just as my evolution, I figured why not use a full arsenal? I think I was limiting myself to a two-pitch pitcher for a while. I've already seen the benefits of using a two-seamer."

Archer's curveball might be the most intriguing change; Statcast™ tracked just 26 hooks after he joined the Pirates, but they featured slightly different movement and less velocity than his slider. We just saw Corbin put up a career season thanks in part to adding a curveball that was essentially a slower version of his slider, so maybe Archer finds similar success.
The back end could provide hidden value
Jordan Lyles' one-year, $2.05 million contract won't rank anywhere near the offseason's headlining acquisitions, but perhaps the Pirates found some value in the veteran journeyman. Lyles is another pitcher who eased off his sinker in favor of a four-seamer in 2018, and found enough success by pairing it with his curveball to post the highest strikeout rate (22.6 percent) of his eight-year career. He was at his best as a reliever once the Brewers claimed him off waivers in early August (3.31 ERA, 2.49 FIP), so perhaps he could be even more valuable as a multi-inning swingman who can piggyback off a back-of-the-rotation starter.
As for those other back-end options, Nick Kingham didn't quite live up to his historic debut last April against the Cardinals, but he has four pitches that posted average to above-average whiff rates, as The Athletic's Eno Sarris pointed out Monday, and could benefit from a change in pitch mix this year. And then there's right-hander Mitch Keller, MLB's No. 16 overall prospect, who took off after a solid showing in last July's All-Star Futures Game and should be in the rotation mix this year.
The only thing missing from the Pirates' starting unit is a true strikeout artist, an element that just about every MLB super rotation boasts in at least one or two spots. But there appears to be enough depth here for this unit to excel regardless, and a full season of Archer -- in a role where he doesn't have to carry the staff -- could help this be the cornerstone of a team looking to get into the crowded NL Central mix.