How do you know that play calling is the problem? How do you know it isn't execution that is the problem?
Plays are being called that don't suit this offense well. We don't have an accurate QB, and we're running an offense that requires accuracy. There needed to be more options, reads, and short routes.
If your Big XII QB is under throwing a WR that is 15 yards downfield by >5 yards, something needs to change, and changing the QB wasn't an option, so the play calling should have changed.