This had to be Mets fans' worst nightmare: The owners, who seemingly can't stop meddling in baseball operations, would hire someone as GM who'd short-circuit the ongoing rebuilding of the farm system in pursuit of short-term wins.
Yes, it is entirely possible that the acquisition of Edwin Diaz and Robinson Cano is the first step toward turning the Mets from a fourth-place team into a playoff team -- even with three teams ahead of them in their own division also improving and spending more money to do so. It's not unreasonable to think that a bit of luck and good health could give the Mets a championship-caliber rotation, that Diaz repeats his historically great 2018 performance, that Cano churns out one last All-Star season, and it all comes together for a 90- to 95-win campaign. It's possible, but it's not likely, and the cost was the Mets' top two prospects, one of whom is the sort of high-ceiling position player they haven't produced from their system since David Wright, because they didn't want to spend more money or, if we believe the rumor mill, give up a 27-year-old rookie.
The Mets are getting two good major league players in Cano and Diaz. The question is not whether they are productive now, but for how long we might expect them to remain at this level.
Cano missed half of 2018 because of a suspension for a positive test for a masking agent. Whatever his reasons for using the banned chemical, he came back and produced about three wins in half a season, hitting .303/.374/.471, rarely striking out, and playing slightly above-average defense at second base. If the Mets are projecting three to four wins from Cano in 2019, they're probably in safe territory. The problem with Cano is that he's 36 years old and signed through his age-40 season. Everybody ages, and baseball players are no exception. Cano is going to decline, and nobody can really predict when that will happen, but it will likely include a move to an easier position (probably first base) and a drop in his batting average on balls in play. He already has next to no range, getting by with great hands and a 70 arm.
In the expansion era, there have been only 14 three-WAR seasons by second basemen age 36 and older, three by Hall of Famer Joe Morgan, per Baseball-Reference's Play Index. Only five of those were over four WAR. This trade is, in essence, a bet that Cano is an exception to historical trends, that he's somehow exempt from normal aging patterns, that Basil Hallward painted his portrait and no one's going to look at it until Cano is 41.
Diaz is an entirely different case, as he just turned in a tremendous, three-win season in relief when he punched out 44 percent of opposing batters in 73 innings, which in itself is on the high side for a modern capital-C closer.
Blessed with tremendous arm strength -- I saw Diaz hitting 95 as a high school senior, but with a delivery barely worthy of the term and thus no command -- Diaz has been good to outstanding since Seattle converted him to the bullpen in 2016, turning in an excellent season that year, a fair season in 2017 with an 11.5 percent walk rate, and then the upper-echelon relief season in 2018.
He works fastball/slider and both pitches are at least plus; two out of the past three years, he has shown excellent control. He's also a reliever, the most volatile category of major leaguers for health or performance. Relievers get hurt -- a lot. And then we sort of forget about them because someone else pops in to replace them. They also don't hold their levels of performance -- since 2000, only two relievers have turned in three straight three-WAR seasons: Joe Nathan and Mariano Rivera. (Bear in mind that Baseball-Reference bumps up its relief WAR with a measure of leverage, so Diaz being worth three WAR last year doesn't mean he'll just add three wins to the Mets with the same production.) A handful of guys have done it two straight years, but three is rare, because pitchers blow out, or lose command, or lose the power stuff that made them elite in the first place. Diaz has four years of team control remaining, but I would put the over/under on healthy, productive years in that span at around two and a half.
Beyond that, the Mets aren't just a closer away from contention. This team won 77 games last year, with Jacob deGrom having an MVP-caliber season and Zack Wheeler making 29 starts and producing nearly four WAR, neither of which is likely to repeat in 2019. They need to plan to add about 20 wins somewhere, and this deal isn't even getting them half of that, while gaining value in a role that may not matter one iota to this team in 2019.
The Mariners get salary relief, shedding the bad half of Cano's contract after he was very productive for Seattle in the first half of his 10-year deal. (Note: Don't sign 30-year-old free agents to 10-year deals.) They take some money back in Jay Bruce and Anthony Swarzak, but it's in the short term; in three or four years, when the M's might be better again, they're free and clear. They also added the Mets' top two prospects, 2018 first-rounder Jarred Kelenic and 2016 first-rounder Justin Dunn -- so you might say New York's amateur staff has done an excellent job in finding two players who would immediately have real trade value.
Kelenic was the sixth overall pick this past June, even though he was a high school position player from Wisconsin, which isn't a traditional state for baseball talent. He's a potential five-tool player if he hits, with a 6 arm (out of 8 on the scouting scale), 6 range, and at least 6 speed, with power trending more toward 7. He has a great body -- athletic and well-built -- projecting to get stronger but not so big he has to move out of center field. He faced better competition the previous summer and showed some idea of the strike zone, which carried over into his spring travel schedule this year and then into pro ball, where he demolished GCL pitching and moved up to the Appy League. He's 19 already, and will turn 20 in July, so he was a bit old for a high school draft pick, and should go right to the Midwest League. If he hits there like he hit last summer, the Mariners might have a superstar in him.
Dunn was primarily a reliever at Boston College, became a starter as a junior, and flew up boards into the first round -- I even had him projected to go to Seattle in at least one mock draft I did that spring. He's very athletic and shows four pitches, with a plus-plus fastball and two breaking balls that show above-average. His changeup is underdeveloped, and he's had a little trouble keeping left-handed batters off base, but not enough to worry about his future as a starter. He also hasn't pitched as much as most college pitchers, so there should be more growth for him as he gains experience and repetitions. His arm really works well and he comes down the hill to get some plane to his fastball too. Pitchers are hard to project, mostly because of injury, but Dunn looks like a midrotation starter with a slight chance to be more because he's so athletic and such a hard worker, with a very high floor in the bullpen.
Seattle also gets Gerson Bautista, a hard-throwing right-handed reliever who throws 94-96 with an average slider at 83-85 and an awful changeup. He's a right-on-right guy who's a half-grade of command away from being a good major league reliever. You might have said the same of Diaz in 2015, although I'm in no way saying Bautista will become Diaz, only that if you have five Bautistas in your system, one of them will probably turn into someone you can use in the ninth inning.
The Mariners have definitely taken on some risk in this deal, hitching their wagon to a 19-year-old outfielder who hasn't seen full-season ball and a starting pitching prospect who has had one good year so far in the pros, but it's the kind of deal they should be making, acquiring high-ceiling prospects with some production already under their belts. Diaz was one of their most valuable assets in trade -- I think Mitch Haniger is even more so -- and they used him in this deal to acquire two prospects who will appear on my top 100 in January. In fact, Seattle was likely to have zero prospects on that top 100 back when the World Series ended, and they have three right now, including Justus Sheffield, with the possibility that they add more if they trade Haniger or Jean Segura. It's real progress for a team whose farm system has regularly landed at or near the bottom of my rankings.