Too many angles against Bears, more than that favor Bears. Nothing at all to favor Bears over Lions. Since as you said, no way to measure the difference between Driskel and Blough, what quantifies the Bears as being a legit 5+ point favorite? Record? Strength of schedule? The spread is simply set to get even action, because the books know, most of the public senses the Bears are the better team, for whatever reason.
The Bears are a wreck. The Lions have nothing to lose at this point and IMO, have a better coach. The Bears are going to clean house after this year.