I hate the single play defense...this game/sim wasn't designed for that...I'm a firm believer JDB should have set minimums for offensive and defensive plays selected (just like he has maximums for each.)
I know rules can funnel specific plays or at least sets but every team should have to call a variety of offensive and defensive plays so the randomness of the game can evolve.
My success on offense is the fact I have no idea what play will be called at just about any point in the game which makes it nearly impossible to scout and defend against it.
I get burned on some defensive play calls but hey, that's football!