This game is NOT skewed towards running. It is skewed towards passing...maybe 60-40 in favor of the passing game....
I think that your "mistake" is somewhat common. Some coaches are not good at "experimentation" in this game, so you just conducted an "experiment" and found something that appears to work. There are certain combinations that work very well and very consistently in this game. There are other combinations that you think should work, but just don't (for whatever reason).
If you have the right talent at the right positions, you can take advantage of certain teams. In this case a SIM is not going to play a prevent type defense...its going to play something balanced or maybe even towards the run. A human may or may not do that.
I know of at least one coach who takes huge gambles with his gameplanning on both sides of the ball. Others hardly change a thing and just overpower you with talent. Many (and this might be you...) have several gameplans, which mix things up and keep the opponent off balance and guessing. If one plan does not work, another kicks in or you make a change at the half. Most teams cannot do well at everything, so if you have a variety of approaches you can likely find the hole in the other teams approach.