Chen (age 29 in 2015): 3.34 ERA / 4.16 FIP / 19.3 K% / 5.2 BB%
Samardzija (30): 4.96 ERA / 4.23 FIP / 17.9 K% / 5.4 BB%
Zimmermann (29): 3.66 ERA / 3.75 FIP / 19.7 K% / 4.7 BB%
The difference isn't in age; Chen is six months younger than Samardzija and less than a year older than Zimmermann. It's not about the qualifying offer; all three received and declined one. When Boras sells Chen as a pitcher who deserves $100 million, he's got a leg to stand on in this market. He can even look back to last year, when Rick Porcello, coming off a similar 3.43/3.67/15.4%/4.9% season, received a four-year, $82.5 million extension. (Porcello was several years younger, but also didn't have the benefit of the open market to shop himself in.)
Let's push it back further than just one season and compare Chen's past three seasons with that of fellow free agent Mike Leake, who has been rumored to be looking for at least $80 million.
Chen, 2013-15: 3.61 ERA / 4.03 FIP / 18.4 K% / 5.4 BB%
Leake, 2013-15: 3.59 ERA / 4.03 FIP / 16.3 K% / 5.9 BB %
Leake is two years younger and gets more grounders while Chen is a fly-ball pitcher, but these performances are nearly identical otherwise. The point is that Chen fits squarely within this group in terms of production, even being able to market himself as the only lefty other than Scott Kazmir remaining on the market, and it's easy to make the argument that he deserves to be paid like it.
Yet it still feels unlikely that Chen actually receives that kind of deal, making him potentially a pretty good value. (A sampling of predictions from four respected sources earlier this winter all expected four years at between $52 million and $80 million.)
So how does a pitcher who doesn't really stand out in any particular area manage to succeed? Chen throws strikes, to begin with. Of the 89 pitchers who threw at least 150 innings in 2015, he was tied with Price for fifth best by landing 53.9 percent of his pitches in the strike zone. Correspondingly, that led to few walks, as Chen's 5.2 percent walk rate was tied for 20th of those 89. He also had one of the 10 highest rates of hitters making contact outside the strike zone, which tends to lead to weaker contact, and the other pitchers on that list -- Leake, Marco Estrada, Bartolo Colon, etc. -- are similar pitchers.
The profile sort of explains itself: Throw strikes, don't give out free passes and don't let the ball get hit hard. Looking at Statcast™ exit velocity, we can see that Chen's average of 87.5 mph ranks 27th of the 147 pitchers who threw at least 1,500 pitches, putting him in the top 20 percent.
Though we don't have Statcast™ data for seasons prior to 2015, if we look at FanGraphs' "Soft-hit percentage," which is calculated differently from Statcast™, Chen is tied for 16th of 54 qualified pitchers from 2013-15. Who's he tied with? Zimmermann. Of course. We're not fully sure yet limiting exit velocity is a skill, but if it is, it explains a lot about Chen -- as does the fact that he induces far more popups than an average pitcher, and popups are basically strikeouts in terms of how often they become outs.
While Chen isn't spectacular at any one particular thing, that's not what he'd be getting paid to be. (Yes, it sounds insane to say that about a contract of $80 million or more, but that's the reality of baseball's exploding economy.) He's a good, solid mid-rotation pitcher, in a world where an elite pitcher collects north of $200 million. Chen is durable, having made more starts since 2012 (117) than Chris Sale, Cueto or Corey Kluber.
Chen almost certainly won't cost what Zimmermann did, and he may not cost what Samardzja did. He's the sort of quietly useful pitcher every good team needs.