So who most needs Ryu for his age-33 season and beyond? The clubs who need starting pitching and seem likely to spend an adequate number of #RyuBucks include the incumbent Dodgers, the Angels and the Twins (that the Dodgers, the team that knows the most about Ryu and how he projects moving forward, are still in on him says much). The Astros also have a post-Gerrit Cole need in the rotation, but they seem committed to a lack of commitment. Whoever takes the risk of note could be handsomely rewarded. Now let’s circle back to those numbers up top. The observant will observe that the author set the baseline for those rankings at 250 innings, which isn’t all that much. That was necessary in order to put Ryu in there and allow this disquisition to issue forth. Yeah, that’s tidy use of endpoints, and that’s because Ryu has dealt with injuries throughout his MLB career. In his early seasons, it was shoulder and elbow problems. Over the last two seasons, it’s been his groin (torn off the bone, no less) and his neck. That’s where the “gamble” part of the headline comes in. 
Ryu in his early days was fastball-heavy. Now, he’s predominantly fastball-changeup with that cutter being his third most common offering. All the while, he’s de-emphasized that troubled slider to the point that he almost never throws it. In essence Ryu now throws five pitches with any kind of regularity, none of them more than a quarter of the time or so. That flattening out of his pitch percentages has helped keep hitters off balance. The cultivation of the cutter has allowed Ryu to attack all sectors of the zone, and the consistent velo gap between his changeup and fastball has allowed him to thrive despite below-average radar gun readings. Throw in Ryu’s dominance at the command and control level, and you’ve got a high-level performer. 
The good news for Ryu and those teams eyeballing him is that there’s a change in repertoire and approach underpinning that skills growth. Prior to the 2017 season, Ryu added a cutter to his already deep repertoire. That was key. Ryu had long struggled to command his chronically fledgling slider, and that left him without a true weapon to his glove side. The cutter is quite similar to a slider, at least in terms of the direction of its lateral movement, and Ryu was able to take to it. 

What makes Ryu great?

A team interested in Ryu would be unwise to think he’s going to continue author ERAs in the low-2.00s over the life on his next contract. It’s possible, yes, but modest steps back in terms of batting average on balls in play and the rate at which Ryu has stranded runners of late are both likely. That said, the word “modest” was just used right there, and the underlying indicators suggest that Ryu has fundamentally pitched at a high level throughout recent history. 
For your edification and viewing pleasure, we present the following table of ERA leaders across the 2018 and 2019 seasons combined, minimum of 250 total innings: 
Let’s, for instance, take FIP (or Fielding Independent Pitching). FIP is scaled to look like ERA but reflects just those outcomes that have nothing to do with fielding — i.e., strikeouts, walks, and home runs allowed. Basically, it’s what a pitcher’s ERA might look like if you gave him average defensive support and average luck. While ERA is perfectly fine when determining a pitcher’s worth in past seasons, FIP, because it strips away a lot of the random noise that goes into ERA, is often the better measure of raw pitching skill. As such, FIP typically projects future performance more accurately than ERA does. Over the last two seasons, Ryu has an FIP of 3.07, which — again among pitchers with at least 250 innings over that span — ranks eighth in all of MLB. Ryu could regress, but the fundamental indicators of FIP suggest that his floor isn’t all that low. Would most teams buy in on a starter likely to give them an ERA in the low- to mid-3.00s? That’s rhetorical, so no need to answer. 
This past season for the Dodgers, Ryu pitched to an MLB-leading 2.32 ERA, and he backed it up with 163 strikeouts against just 22 unintentional walks in 182 2/3 innings. Throw in his 1.97 ERA from his injury-shortened 2018 and you get that sparkling figure above, which lags only deGrom’s. 

Why would it be a gamble to sign Ryu?

The headline of this electronic dispatch includes the name “Hyun-Jin Ryu” in it, so you can probably guess which of those five names we’re going to talk about. Yes, Ryu has been walking with the modern gods over these last two campaigns. Ryu is also a free agent who’s still looking for work.
Yes, the team that signs Ryu will be taking a risk on him in light of his health history. We don’t project injuries very well in baseball, but there’s a couple of reasons for optimism in this particular case. First, nothing predicts injuries in future seasons like injuries in prior seasons. Ryu in 2018 was relatively healthy, and in fact his 182 2/3 innings were his most since his rookie season of 2013. As well, he hasn’t had significant arm troubles since 2016. In light of Ryu’s entire injury history, those are encouraging trends (perhaps “trendlets” would be more accurate). 

Which teams could roll the dice?

Of course, Ryu’s 2018-19 success is at odds with his earlier history. Coming into the 2018 season, Ryu owned a career ERA+ of 109. That’s good — nine percent better than the league average on a park-adjusted basis. Since then, though, he’s put up an ERA+ of 184 — i.e., a park-adjusted ERA that’s a whopping 84 percent better than the league mean. Suffice it to say, that’s a whole other level. This of course circles back to the skepticism hinted at above that a pitcher can level up to such an extent in his thirties in a sustainable fashion.