By your own rule of Brady being +5 wins per year, which is actually pretty fair to say. Any team with Brady gets approximately 5 extra wins per season, compared to one without. Their records without him those years are 9-7, 8-8, and 7-9. It is obviously not perfect or exact, nor are those terrible records by Bills standards. Those numbers are average and beatable, which is a HUGE fall from grace, because with Brady they are one of, if not the best team in the NFL