Law: The Mets fail to learn from history. Will the Edwin Díaz deal doom them to

The Mets were going to end up hunting for a new closer, or high-leverage reliever, if they lost Edwin Díaz to free agency. He was the best reliever in baseball this past year, worth 3 WAR by both major sites’ methods, and his FIP of 0.90 was the fourth-lowest this century for any pitcher with at least 50 IP. He’s great. The Mets’ decision to give him five years and $100 million is anything but.

Díaz’s season was incredible, but relievers who do this just don’t repeat it. The three players who had lower FIPs than Díaz did all saw theirs go up by over a full run the next year. Eric Gagné never came close to that level of dominance again. Aroldis Chapman was still elite, just not as much as so in his peak season, for the next two years and then dropped to merely above-average. The third, Craig Kimbrel, did it one more time, five years later, and then headed over the cliff.

The list of the best relief seasons of this century is full of good pitchers who had their best years and never matched it, as well as some flash-in-the-pan types. Almost nobody has held something close to this kind of performance for more than three consecutive years. Even those who got to three straight years did so before free agency.

Only five pitchers this millennium have thrown at least 50 innings with a sub-2.5 FIP in four or five consecutive years: Kimbrel in 2011-14, Greg Holland in 2011-14, Kenley Jansen in 2013-17, Chapman in 2012-16 and Andrew Miller in 2014-17. (Pedro Martínez did it too, if you needed more reasons to worship at that altar.) Miller is the only one of those relievers to do any of it during the years covered by a free-agent contract. All were substantially worse in the five years after those runs of excellence.

This century, there have been, by my count, 20 contracts of four or five years handed to free-agent relievers, not counting the new deal for Díaz. Jansen, Chapman and B.J. Ryan received five-year deals, and the remainder were all for four years. One of the deals, Raisel Iglesias’, is still underway with 1.6 WAR in year one — although most of that came after the team that signed him, the Angels, dumped him and the contract on Atlanta midway through year one. Jansen’s and Chapman’s immediately followed the ends of those five-year periods I mentioned above.

Of the other 19, nine of them resulted in 4 WAR or less from the pitcher over the course of the deal, regardless of teams. That includes Brett Cecil (minus-0.5), Justin Speier (0.8), Drew Pomeranz (1.8, and out for all of year three due to injury), and Scott Linebrink (1.8). Only three of the deals resulted in an average WAR of at least 2: the Kimbrel deal originally signed with the Padres, the Miller deal with the Yankees and Mariano Rivera’s contract from 2001 to 2004. That Rivera deal is the only four- or five-year contract given to a reliever who produced at least 10 WAR over the course of the deal. One out of 19, and it belongs to the greatest short…