I think it is a decent trade. Stockpiling prospects to trade later was the long term plan. Biggest worry about Paxton is that he is injury prone. However, if you look at our lefty starters they are either too old (CC/Happ), or too inexperienced (Jordan Montgomery). And think they may sign Corbin too.
While I'm not a Yanks' fan, I agree that this was a good trade. When he's on, Paxton can be filthy. And Baseball Prospectus speculates that he might only now be peaking b/c he had injuries early in his career that curtailed his usage. The one question is, how does he react to the bandbox that is Yankee Stadium?
Yes, they gave up some good potential wild cards in the deal, but the reason you build a deep system is for trades like this.