I don't see how playing terrible fundamental baseball isn't at least partially the manager's fault. What this season has clearly proven is that the FO has no idea how to run a baseball franchise and their choice of manager, although not their biggest mistake, is far from ideal.
Ultimately, I don't think a different manager would have made a whole lot of difference but it's foolish to dismiss Gibbons from doing anything wrong.
This season has been a complete embarrassment and the manager along with the GM and that clown of a president all need to be held accountable.