The real reason Danny Ainge should be taken to task for last year is that his complete and utter FUBAR of an off season did not effect just last season. I tried to relay this through some of the stuff I said last summer. If instead of concentrating on Posey to the point of ignoring all other options and then being left with flotsam and jetsam thereafter, he had started with a philosophy of trying to get proven veterans to fill roles, he would still have one or two of those players on this roster that would make this off season easier.
It's easy to say that Danny didn't cost us a championship this year with his bad off season because of injuries but did he cost us future championships because we don't have good role players on this team. By taking low risk, high reward risks across the board and then compounding that philosophy by bringing back Tony Allen he has left only one player from last years off season additions that can still be a contributor in the foreseeable future. And even then, Eddie could opt out and go elsewhere, though I think that unlikely.
So instead of trying to wrap up a Barnes or Pietrus or Mason for a few years, he tried the Miles, POB, Allen and rookies route. Now instead of a proven veteran returning to the team next year he has Tony, Eddie, JR, and Walker and has to hope and pray one of this year's rookies can take a major leap to viable NBA player next year.
So this year he has to actually do the work of two off seasons but with the money of only one off season. By squandering the MLE money last year and taking chances on rookies and projects he threw away an opportunity to add one very good, proven veteran for multiple years that could contribute even in the playoffs. Because really, not one person Danny added last off season made any significant contributions this post season. Eddie was good a couple of games but wasn't really a consistent playoff contributor.