I agree the play calling on offense has been quite poor this year, at times just plain awful. However, the head coach is on the head set and can veto or say run the ball, etc. The head coach is involved in the offensive game plan leading up to the game as well. Firing McIlwain may not solve the problem. At times the defensive play calling has been quite bad too. I'd say keep the staff in tact if you can. If you want to make replacements, look at the offensive and defensive line responsibilities.
The bottom line is the team is not physical. They're not tough physically or mentally. They're not in good condition either. They're not hungry. They're not motivated. That all falls on Saban.
My guess is Saban has figured this out and will fix the problems going in to next season. I feel they will likely go undefeated or have 1 loss next season. At least they should with all of the talent they have coming back next year. Their defense should be the best or near the top. They will have a tough schedule again.