With the acquisition of Aroldis Chapman, the Yankees are building a bullpen to rival the Royals. Now, the other stuff surrounding Chapman makes the comparison a little difficult - will he get suspended? If so, for how long? Etc. Plenty of others have written about the place of domestic violence in this trade, so I do not want to get into that.
I believe Shaun posted this image in a comment somewhere, but I'll repost it here to remind you all: The Yankees have a better back three than the Royals now.
On a total fWAR basis, on an ERA basis, on an FIP basis, on an xFIP basis, and on a strikeout basis, the Yankees' new back three beat out the Royals' back three. Handily. Or do they?
Surely Wade Davis is the best of the bunch. Yes, he has higher peripherals, but he is about as automatic as it gets. To get a more accurate comparison, let's assume that Chapman plays in 2016, but he misses the requisite amount of time to stay under Yankee control through 2017 (about 46 games I think). That's about 28 percent of the season. In those games, Chasen Shreve is probably the next guy up; Justin Wilson and Adam Warren were traded.
Shreve was not good last year. He had the highest walk rate (BB%) of any qualified reliever. His 3.09 ERA hid a 4.92 FIP and 4.23 xFIP. Inserting his numbers for 28 percent of the season probably brings Chapman's "slot" numbers closer to Soria's or Herrera's numbers. If Chapman misses more time, this makes the comparison even more favorable for the Royals.
So that's two spots that could compare pretty favorably for the Royals, leaving one left. For the sake of argument, let's say that the Shreve/Chapman hybrid matches up well with Soria. Davis beats out either Miller or Betances; take your pick. Herrera is the last one on the Royals' side to compare to whomever you did not choose. This is where Herrera's new slider comes in.
He really started using it in the postseason. Jeff Sullivan's linked article above noted its usage at about 25 percent up to that point in the postseason after being used less than 10 percent of the time in the regular season. When it was all said and done, Herrera faced 54 batters in the run to the championship and struck out 22 of them. He walked only three batters. This translates to a 40.7 K% and 5.6 BB%. That puts him right up with Miller and Chapman in strikeouts WHILE walking fewer batters.
Of course, this occurred over just 13.2 innings. There is some small sample size variation here, but the projections seem to buy the improvement. Herrera's Steamer projected strikeout rate of 24.4 percent would be his best since 2013 and second-best overall of his career.
But what if you're optimistic? What if you think Herrera's new slider will catapult him into uncharted waters? What if he can really control the thing? In that case, a 3.26 ERA and 3.38 FIP, as projected by Steamer, seem rather pessimistic.
I'm not suggesting that Herrera will maintain a 40 percent strikeout rate and 5 percent walk rate. If the slider is for real, though, I do not think a 30 percent strikeout rate is out of the question. Herrera's company in that realm would be guys like Drew Storen, Ken Giles, and Trevor Rosenthal, except with a better BABIP. Those three guys' ERAs ranged from 1.80 to 3.44. Their FIPs ranged from 2.13 to 2.79. That's Betances/Miller range.
So there you have it. The Royals' back three when viewed through the rosiest of rose-colored glasses is still better than the Yankees' back three. We don't even need to consider depth.