This is pretty much my feeling. You can have a cookie cutter defense against Western Kentucky and blow their doors off. You can do that type of thing against Purdue and win comfortably. You might be able to beat Penn State at home during a night game like that too.
But Oregon, Texas, Georgia, Alabama, and the like will carve you to pieces if you show up with exactly what it is they've seen on film all season. You've got to mix some things up and make something happen, even if like you said you drop a DE in the flat and bring a LB from a different angle... SOMETHING!