Dallas Keuchel did something in 2018 that you just about never, ever see anymore. It might be the last time you see it for a while.

It's partially that Keuchel threw over 200 innings, which is a rarity itself these days. Just 13 pitchers got to 200 innings last year, the lowest full-season number in baseball history. You know all about "bullpenning" and "the opener" and the times through the order penalty and that complete games are virtually extinct. That much isn't news. Two-hundred remains a notable -- if endangered -- number.

But it's more than just about getting there. It's that Keuchel threw over 200 innings that were more "good" than "great," the type that made him more solidly above-average than it did an ace. In a previous era, it would have given him the description of "workhorse" or "innings eater." Now? It makes him a unicorn. Aces still get to 200. Other guys ... don't.

• The latest on Keuchel's free agency

It becomes a little clearer when we look at who those 13 were last year. They were either aces or pitched like one. There's Jacob deGrom, Max Scherzer and Justin Verlander. There's Aaron Nola, Corey Kluber, Gerrit Cole and Patrick Corbin. There were new names like Miles Mikolas, Mike Clevinger and Kyle Freeland, and reliable top-end starters like Zack Greinke. Great pitchers who stay healthy get to throw lots of innings. That much hasn't changed.

Clevinger might not tip the scales for you as an ace, perhaps because he might be the fourth-best starter in a stacked Cleveland rotation behind Kluber, Carlos Carrasco and Trevor Bauer. But he also threw 200 innings with a 3.02 ERA. This becomes a little clearer if we look at ERA+, a stat in which 100 is "league average," and Clevinger's 145 makes him "45 percent above average." You can see where he ranks within this group.

As you can see, the top 11 had stellar seasons. Then there's a gap before Keuchel's good year, and another before you get to James Shields, who at age 36 put up a 4.53 ERA in what may have been the final season of his career.

Another way of saying that is that of the 13 pitchers who threw 200 innings last year, just two came from pitchers with ERA+ marks between 90 and 110, or "within 10 percent above or below average" -- unsurprisingly, another all-time low.

That means only 15 percent of the pitchers who made it to 200 innings last year were non-aces, just "workhorses," which is how we'll define this class of pitchers -- 200-plus innings pitched, ERA+ between 90 and 110. That 15 percent is the second-lowest in baseball history, behind 1939, when only three of the 27 200-hundred inning men (11 percent) were "workhorses." (The 101-loss 1939 St. Louis Browns let 21-year-old Jack Kramer throw 211 2/3 innings of 5.83 ERA ball. He may have been their best pitcher.)

The heyday of this kind of pitcher came in 1980, when 55 percent of the 200-inning pitchers were "workhorses" -- guys like Jack Morris, Dennis Leonard and both Niekro brothers, Phil and Joe. If we look back at the last 40 years, we can see that it is indeed not just about the total number of 200-inning guys falling, it's that the rate of non-elite 200 inning pitchers has fallen as well.

(Note: The shaded portions of the line in the graphic above represent strike-shortened seasons.)

It's an interesting trend. It's harder than ever to get to 200 innings. It's harder than ever to get there without also pitching like one of the best pitchers in the sport.

That's not a knock on the still-unsigned Keuchel, of course, because there was a time that he would have been in the "ace" category, like when he won the 2015 American League Cy Young Award by putting up a 2.48 ERA (157 ERA+) in 232 innings. It's just that he wasn't quite that guy in 2018, comparatively. Comparing his '18 against his '15, Keuchel's sinker velocity was down from 90.1 mph to 89.1 mph, his strikeout rate dropped from 24 percent to 18 percent and his grounder rate dropped from 62 percent to 54 percent.

That's still a good pitcher, obviously. As you can see by his Statcast peripherals, while Keuchel's fastball velocity is low (only 7th percentile), as is his strikeout rate (17th percentile), his hard-hit rate, exit velocity allowed and expected weighted on-base average numbers are all around the 67th percentile, which sounds about right -- it means he's better than about two-thirds of qualified pitchers.

As we said above: Solidly above-average, if not quite ace-like, with his impressive durability (three seasons of 200-plus innings) somewhat tempered by shoulder trouble in 2016 and a neck issue in 2017. Still, that's a pitcher the Braves could use, as their young rotation is already dealing with health problems. It's one the Twins could use to try to catch Cleveland, or the Phillies to add depth in a brutal NL East, all while a return to Houston may still be on the table.

Still, this is likely part of why he remains unsigned weeks after Spring Training began, because a sport focused on velocity, missing bats and future performance sees him as the solid workhorse he projects to be for the next few years, while Keuchel is probably selling himself as a Cy Young-winning World Series champion -- as he should.

Regardless of where he ends up landing, Keuchel might be the last of his kind for a while, especially with the unsigned Shields unlikely to get to 200 ever again. It's hard to throw 200 innings in a season these days. It's even harder when you're good, not great.