I think they got caught unaware of the changing market. They went into the off-season thinking they'd be able to add more players w/o hitting the tax. Many of us thought that too: sign Hamels for cheap, save money by going after Wheeler rather than Cole or Strasburg, and Didi rather than Rendon or Moustakas (who they might have wanted if he was affordable). Add one reliever. And then maybe even a spare bat. Bring back Smyly on a minor league deal.
When Middleton said that last year, he was theoretically talking about adding that last, Halladay-like high-$ piece to a serious contending team. When MacPhail said that yesterday he was recognizing that to even make a couple of modest trade deadline moves they are going to have to pay the tax. They may yet have to pay it now (wouldn't take much: lose both arbitration cases, have two infielders and one relievers with seven figure salaries and incentives make the team. In the end it's possible they will go with a rookie over Liriano (especially now that they've signed Hunter) and a light-hitting utility guy over Harrison or Walker just to save $2 million).
If they fail this year it will be most interesting to see if MacPhail is held accountable. But for now I also buy what they are selling: that last year's team legit had 87-90 win talent, so the new additions/manager should keep this year's team at that level too. It could just go wrong (again) so easily.
Middleton doesn't escape blame here though. He pushed for more spending and an accelerated timetable. Having failed to improve that much last year to even expect a "deep playoff run" this year rather than simply making the wild card (which most people assumed was the ceiling last year, though the Nats obviously did a lot more with it) is a lot to ask - and probably did require paying the tax and/or trading away prospects.
Who knows, Kris Bryant still hasn't been traded.