I know JG sounds like a poster boy of cliches, however his teams almost always play hard for him.
To me JG is probably fine as a head coach, especially given the Jerry dynamic etc, but he has to have high quality coordinators who know their Xs and Os and will make the necessary game time adjustments. That is sorely missing on this team, especially on offense.
I think JG's lack of knowledge also shows up with some of personnel decisions, and how slow they are to make changes when guys struggle or to find roles for younger players.
Another thing JG doesn't get credit for is the change in direction on how the organization goes about building the roster. Jerry probably drafts Manziel if it isn't for JG, McClay and Stephen. I might be wrong but it feels like those 3 are on the same page in turns of the direction of the roster for the most part. I find it hard to believe the HC doesn't have a lot of input in that philosophy.