It's no secret that the reigning World Series champion Chicago Cubs have underwhelmed in their title defense thus far this season, wallowing 5.5 games behind the upstart Milwaukee Brewers in the National League Central standings while suffering a never-ending litany of disappointing performances from both their promising young core and their veteran stalwarts. The Cubs' scuffling is no fluke -- per numberFire's nERD metric, Chicago isn't even the second-best team in their division.

Today the Cubs showed just how anxious they are to keep their heads above water, shipping a substantial prospect package across town to the Chicago White Sox for veteran lefty Jose Quintana in an out-of-nowhere blockbuster.

The centerpieces of the deal are the Cubs' two highest-ranking prospects, per MLB Pipeline -- outfielder Eloy Jimenez and right-handed starter Dylan Cease. Jimenez is growing into his 70-grade raw power in High-A, posting gains in isolated slugging (ISO) in each of his past two seasons, all while flashing improved plate discipline (9.8% strikeout-minus-walk rate in 174 plate appearances) to go with his plus contact skills.

Jimenez put on a show at the recent MLB Futures Game, ripping a double down the line and flashing some leather out in right.

Meanwhile, 21-year-old Cease appears to be rounding into form, as well, despite a short stint on the disabled list for a minor ankle injury. A classically tantalizing high-velocity prospect, Cease has touched 101 miles per hour on his heater while leveraging his power curve for massive strikeout totals for High-A South Bend. However, he comes with some control hiccups as his current 4.5 walks-per-nine rate on the season is actually a career-best mark.

Indeed, the Cubs surrendered no small bounty here, with Jimenez and Cease both appearing on the verge of a promotion to Double-A, to say nothing of the two additional prospects who round out the deal, first baseman Matt Rose and infielder Bryant Flete.

But did the Cubs give up too much for the veteran lefty? How badly did they really need help for their starting rotation?

Staff Infection

There's really no getting around how underwhelming the Chicago staff has been this season. Per numberfire's nERD metrics, veteran lefty Jon Lester is their most productive arm, ranking 31th (16th among starters) in our MLB Player Power rankings. Even further down the list is erstwhile ace Jake Arrieta at 45th, with his 4.35 ERA and 3.11 walks-per-nine hardly soothing the fears that cropped up during his disappointing Cy Young follow-up season last year.

But it's not the front-of-rotation woes that have truly troubled the Cubbies in 2017. No, where the Cubs have suffered this season is in the back end of their staff.

Surprise 2016 Cy Young contender Kyle Hendricks has regressed with a vengeance, toting an middling 4.09 ERA while seeing his walks-per-nine rate balloon from 2.08 last year to 3.06 in 2017. Hendricks appears to have totally lost the feel for his go-to changeup, with wild movement trends incurring apathy from opposing hitters, who are whiffing substantially less at the pitch and offering much less often at Hendricks' changeups outside of the zone.

The 27-year-old appears to have no choice other than to hang the changeup out to dry to stay alive in counts, but the approach has backfired: Hendricks is allowing over 92% in-zone contact on that change, up from under 75% last year. We're not talking light tappers, either -- check out the .226 ISO allowed on that pitch, compared to a .111 career mark.

Meanwhile, Hendricks' struggles have been a walk in the park compared to the trials of once-reliable veteran John Lackey, who headed into the break carrying the second-highest fielding independent pitching (FIP) mark among qualifying MLB starters (with a bout of plantar fasciitis to boot).

We appear to be seeing an exaggerated version of Lackey's last truly subpar season, the 2014 campaign where he split 198 innings of 3.82 ERA work between the Boston Red Sox and St. Louis Cardinals. That year the veteran righty saw a major dip in the effectiveness of his secondary pitches, with his sinker and curveball surrendering 132 and 198 weighted runs created plus (wRC+) respectively. Well, this year the bottom has completely fallen out, with those pitches both surrendering over 200 wRC+ and over 1.100 each in opposing on-base-plus slugging (OPS).

Indeed, the Cubs' back end has been so balky, and its frontline starters so relatively uninspiring, that their six qualified starters (the four players mentioned above, along with Eddie Butler and Mike Montgomery) have combined for only 4.8 total Wins Above Replacement (WAR), per FanGraphs -- that's less than Red Sox ace Chris Sale has earned on his own.

Is Quintana Worth The Gamble?

The question remains whether the player the Cubs unloaded the farm for offers enough to turn around the team's ailing rotation.

Perhaps the White Sox's bounty of a return for Quintana seems, at least on the surface, a little excessive, given that the 28-year-old lefty appears to be having the weakest season of his career in terms of surface results.

Indeed, the normally clockwork-steady Quintana is currently sporting a 4.49 ERA, which would represent a five-year-worst mark by almost a full run. The two culprits here appear to be a major spike in walks -- up to 3.5 walks-per-nine this season compared to a career mark of 2.4 -- as well as a notable uptick in homer-per-fly-ball-rate, with a near-13% mark representing a career worst by a fair margin.

Quintana's pitch-type data appears to lie the bulk of his 2017 struggles at the feet of his sinking fastball, which has gone from surrendering a .621 OPS in 2016 to a whopping 1.086 mark across 360 pitches this season. The thing is, Quintana hasn't really needed his sinker to thrive in previous seasons -- there's a fairly notable fluctuation in wRC+ allowed on that pitch over the previous five seasons: 97, 116, 166, 106 and 83. His ERA in that especially poor 166-wRC+ season, when he surrendered a near .900 OPS with the sinker? 3.32 in 200-plus innings, with a 2.81 FIP for good measure.

Meanwhile, Quintana's fastball-curveball arsenal has arguably never been better. The curve, in particular, is showing some of strongest results of Quintana's career, including a five-year high in swinging-strike rate and a contact rate of 61% that is 10 percentage points lower than his career mark with that pitch.

And while Quintana has never been one to flash an overpowering fastball, his fourseam has been as effective as ever at suppressing quality contact, boasting a career-low .097 ISO and a four-year low line-drive rate. A near-24% strikeout rate with the heater, building on his modest 20% career fastball mark, doesn't hurt either.

The inspired fastball-curve combo probably has a lot to do with Quintana's eye-popping strikeout rate gains, with the southpaw's surprisingly robust 9.4 strikeouts-per-nine rate posing a sneaky sub-narrative to what might otherwise appear to be a "down" year.

A Worthy Addition

With reports of Quintana's decline clearly overstated, the Cubs appear to have pushed their prospect chips all in on a worthy number-two starter to help stabilize their inconsistent staff. In fact, the Cubs are catching Quintana in the midst of a bit of a resurgence -- he's strung together 40 innings of 2.70 ERA ball (certified by a not-too-shabby 3.40 FIP), all while continuing his whiff renaissance by striking out over 10 per nine and keeping the ball in the park to the tune of less than a homer per nine over that span.

Here he is dominating the Minnesota Twins over 6 2/3 shutout innings back on June 22, a start in which he fanned nine without issuing a free pass.

Armchair prospect hawks will likely claim that the Cubs gave up too much to secure the services of a non-ace, but bear in mind that not only is Quintana a 28-year-old who brings with him a five-year track record of consistent performance, but he also happens to carry a very team-friendly contract, with the lefty signed through 2018 with club options for the two seasons that follow. In all, Quintana is owed just $29.8 million over the next three seasons (assuming the team options are exercised), quite a deal considering what top-tier arms command on the market.

Give the Cubs credit for recognizing a need and paying up to resolve it. It's similar to what they did this offseason when they acquired relief wizard Wade Davis for young outfielder Jorge Soler -- dealing from a strength to address a need. If Quintana continues his strong June work and the Cubs other starters follow suit, the reigning champs could very well be making some serious noise in October for the second straight season.