If you're prone to falling too deeply in love, too quickly, with your team's prospects -- as I most certainly am -- then your first blush at a trade like "Jacob Nottingham and Bubba Derby for Khris Davis" is going to be "Nooooooooo!!!! I was so attached to Nottingham even though I sometimes have to look up his first name to remind myself and I think he's white or maybe I just assume that, man I remember how surprised I was when I learned that Tyler Ladendorf was black."
Yet even as someone who hates seeing promising prospects dealt, I think the A's have made an excellent gamble in swapping two exciting, but highly unproven, prospects for a somewhat unproven breakout candidate in Khris Davis.
First a clarification:
I do not suspect that the A's made the trade out of any particular skepticism over Nottingham's ability to stick at catcher. More likely, they wanted Davis enough and could not get him without trading someone as promising as Nottingham. What I think the A's did know is that Nottingham still has multiple hurdles to jump, from sharpening his defensive skills to mastering AA and AAA, and that he was not going to be a factor until 2018. Similarly, Derby is far enough from the big leagues that the risk of hitting a wall at higher levels or the dreaded arm injury made him another "ouch, but risky enough to part with" prospect.
As far as what the A's got back, in Davis Oakland has acquired a pretty typical target for the way this team is structured. Davis is young (20s, anyway), cheap, and cost-controlled, ready to contribute immediately, with the talent to be excellent but not yet the track record to command a Chris Bassitt or Franklin Barreto in return. He is exactly what the A's are always seeking: someone with the talent to be a significant contributor but without the street cred that makes him expensive.
In some ways, Davis is similar to Mark Canha: he profiles as a very average defender but has a powerful bat and considerable offensive upside with no guarantee of achieving it. I think the redundancy is fine. Just as the A's are not building a 5-man rotation but rather a rotation for 162 games, they are not building an outfield of "3 guys" so much as they are building an outfield -- and 1B, and DH spot -- that can sustain them over 6 months.
Given Canha's ability to play 1B, the likelihood that at least four outfielders will see appreciable playing time, the DH spot, and the fact that Yonder Alonso is under contract for only 2 years (compared to Davis' 4 and Canha's 5), there may be a slight glut but there is ample room for every player who is productive. The A's should be so lucky as to have 6-7 guys so productive you would want to play them every day.
So the A's have lost a "possible catcher, possible 1B/OFer, potentially excellent hitter" and gained a major league ready OFer with 4 years left on his contract -- someone who is basically a 4-years-advanced version of Nottingham if Nottingham does not make it to the big leagues as a catcher. Losing Derby is a bummer but hardly a crisis, as Oakland has Sean Manaea, Dillon Overton, Raul Alcantara, Casey Meisner, and Daniel Mengden, among others, ahead of him on the depth chart.
Maybe Khris Davis breaks out this season and maybe he doesn't. Perhaps Jacob Nottingham sticks at catcher, perhaps he doesn't. Bubba Derby quite possibly rises quickly through the minors and quite possibly succumbs to TJS and is never heard from again.
There is no certainty in these kinds of deals and much risk. But judging the trade at the time it was made, one has to think the A's have gotten better for 2016, with a player under contract through 2019, and may well have gotten the best young player of the three. It's hard for me, even as someone too attached to Nottingham, to think this wasn't the right deal to make.