The issue here is we are only seeing the end result (X for Y) and have absolutely no idea on what was on the plate for the Blue Jays to pick from.
If we knew, and there was a prospect from another system or Yankees themselves who would have fit our repertoire better, then sure you can adamantly claim this was a worse (not bad) trade. But we don't, and suffice to say, we have to accept that what we got was the best we could for Happ. Maybe they could have been more creative, but time was running out and they needed to move him for something.
We could have traded him at the start of the trade window when his value was the highest, and perhaps got a better return. But Shatkins took a gamble to increase his value over the next 2 or 3 starts, where Happ (unfortunately) blew himself up. Imagine if he did not and produced consistently sharp #s, well his value would be higher than it was at the start of July and we could've aimed for a blockbuster deal.
Finally, why are people set on throwing Drury/McKinnel under the bus? Prospects/players *can* get better (Bautista for example, clearly). We have good years of control on these two young guys, and they have as much upside as downside. It isn't like we are going to be competing next year (or the year after that). If these guys can provide even a bit of consistency of being an average/above average player, we can leverage them for pieces in another trade or, who knows, maybe they'll fit well in to the system.