I don't think it is. In fact, I've been pretty vocal that Beane is the biggest issue. He's let this roster get old and expensive. Before this season started, I caught all kinds of heat for saying that everyone should be prepared for major injury issues again this year.
There are very few key players on this roster who aren't either old, coming off serious injuries, or both. Now Von looks washed, Tre is done, Jones is done, and we're not even halfway through the season. Poyer and Hyde can still get by on veteran savvy, but they're clearly shells of their former selves, and that's only going to get worse as the season progresses. That's a GM problem rather than a coaching problem. (I do acknowledge that it could be a lot of McDermott getting involved in personnel decisions, but it's still not a function of coaching.)