Very late to this thread due to not spending too much bye week time thinking about the Bills. Not good for my mental health I'm sorry to say.
I am in complete agreement with the basic premise however. The issue is talent and that is the GM's job. I don't think McDermott is a great game day coach, but he's better than many coaches overall. The coordinators are below average and I don't know enough to comment on the position coaches. I think Beane got the Allen pick right and not nearly enough other than that. This fact has finally really come to roost this year, and now the coaches have got to dig us out somehow. I'm a little hopeful but not very optimistic.
One thing that I've considered is Beane should turn over drafting to someone else. His cap management is ok, I'm not a big fan of locking up mediocrity long term but some of the contracts are defendable. His free agent signings lately have been mixed at best but a while ago were good (Poyer and Hyde great examples). But his drafting has been a big problem. Maybe some is bad luck but eventually luck settles out and we have plenty of data now.