I don't think Gailey wants to fire Edwards immediately because, record-wise, Buff is far from out of contention. A staff shake up now might be interpreted by some in the locker room as giving up on this season already - which would probably assure their current free fall would continue through the rest of the season.
That said, i agree with you, i've seen enough of the Edwards hybrid experiment and think he should go after this season. The talent level on D is inadequate for anything other than a base 43 at this point. We don't even have enough decent DBs to field a competent nickel/dime defense on passing downs. Unless you're playing Denver every week, that spells death in today's league. Here's hoping Aaron Williams makes some big strides in the next few weeks.