the stats you listed they were in the bottom 1/3 of the country. The only reason they don't have more yards against them is other teams are playing clock management for at least 1 quarter.
Yes the offense has been worse, but that doesn't mean the defense is OK. Both have been bad imo. For 4-5 games the defense has been OK, the rest they were bad.
I agree that we really don't know if Detmer is that bad of an OC right now. Results have been horrible, but is that all his fault? I honestly don't know.