I clumsily tried to sum up all my thoughts in the title, but here, one by one for the 4 main players traded -- David Phelps, Nathan Eovaldi, Martin Prado, and Garrett Jones -- is why I love this deal. 1. Phelps won't be missed. If you look up "replacement-level starter" in a dictionary, Phelps might be the photo you see: WAR of -0.1 in 2013, 0.0 in 2014; career (2012-14) ERA of 4.34 as a starter (average A.L. ERA in '14: 3.82). If you did the surgery from "Face-Off" and put Phelps' mug on Bryan Mitchell or Chase Whitley, their own wives couldn't tell -- which basically is the definition of replacement-level: you can lose the guy, and sub in an above-par AAA'er, with little to no difference.
2. Eovaldi, not Phelps, is the rarely available commodity. He's a SP who (a) is 24 (25 by opening day), (b) throws hard (avg FB of 95.7, 4th in MLB), (c) has control (2014, 1.9 BB/9), and (d) has improved his control a lot (3+ BB/9 to 1.9 in 2014), K rate somewhat (1.5 yrs at 5.9-6.0, then 6.6 and 6.4), and overall performance a ton – his yearly FIPs form a straight downward slope: 4.35, 4.13, 3.59, 3.37. His weak K rates are odd for a flamethrower, but given his age, high heat, and modest but real K-rate improvement to date, there's reason for optimism about his ability to miss bats. Honestly, if he had high K rates already, he'd already be a totally unavailable ace. So the Yanks landed a 24 yr-old whose low-mid 3 FIPs give him a #3 SP floor (well above Phelps), an easy shot at #2 SP performance, and a realistic shot (if his K rate rises to match his stuff) at being a #1. Joel Sherman's "worry ... Did they just get younger version of Burnett. Great stuff, but can’t execute consistently" – is not a bad comp, but less a "worry" than a pretty positive worst-case scenario: starting at age 25 (Eovaldi's 2015 age), Burnett averaged almost 3 WAR/yr through age 32; yeah, I'd take that as the "worry" case of Eovaldi not fully putting it together. The difference between Eovaldi and a replacement-level Phelps is easily 2-3 WAR, so compare the lose of Prado:
3. Prado is nice – but a fair price for Eovaldi, and he was blocking two kids who earned a shot. Yes, Prado likely could outplay the winner of a Refsnyder/Pirela 2B competition; if Prado is worth 3 WAR, assume the winner of Ref v. Pirela is 1-2 WAR worse (could be better, could be worse). But smart teams give shots to 24 year-olds who ace AAA; if just one of Ref/Pirela is legit, you've locked down 2B at low cost though about 2020. With the unusual luxury of two deserving youngsters ready for the same position the same year, we're not stuck if one bombs. Keep in mind (hat tip: Michael & EJ) that just months ago, Prado cost only a power hitter without a position who struck out over once per game at A & AA (Peter O'Brien), so it's quite a flip to package him with a replacement SP and land a strong 24yo SP.
4. Jones is only a useful spare part - but a perfect fit. He's an average hitter but with a helpful platoon split for Yankee Stadium and for splitting time with A-Rod: the past 2 yrs he's OPS+'d 98, but OPS'd .730-.749 vs RHP. He's a butcher in the field, but (a) Chris Young already fills the defensive-replacement role, and (b) Jones can mostly DH, plus fill in at 1B if Teixeira needs to rest against a righty (against LHP, Headley might move to 1B while A-Rod tries to find his 3B glove). In a sense, WAR doesn't tell the whole story, because the Yanks' needs and stadium let them exploit what Jones does well (power-hit vs RHP) while minimizing what he does badly (hit LHP, and field anywhere).