McCown is a great example of why every team should have a competent backup QB. If the Packers had a backup QB like McCown, they'd be at the top of their division.
Really no drop off from McCown to Cutler. If anything, you could make the argument of McCown over Cutler. I don't think I'd go that far, but McCown is a top 3 backup QB, and could probably start for a handful of NFL teams.