"At all responsible" is fine. Its the blame every bad thing on McD, but attribute every good thing to Beane.
And to address lack of player development - Poyer, Hyde, White, Milano, Johnson, Edmunds, Wallace, Benford, Bernard, Bishop, etc. There have been plenty of examples of young guys that developed in McD defense. The issue has really been the free agents have not had the needed impact and the recent drafts, which I would argue Beane likely had more control over than the early drafts, have been much less productive. Plus overpaying second contracts on guys that are good but not great players.