What's the secret to a good defense?

I've had lots of success in recruiting, consistently pulling in top-30 classes with a top-10 class every few years. So needless to say, there is a lot of talent on the field. However, for some reason my defense consistently gives up 30+ppg. I've edited the DC scheme, I've given depth chart and strategy control to the head coach, but somehow just can't get over the hump. There has been one season that was 10-2... all the rest have been 6-6 or 5-7, even though the makeup of the roster (from a ratings standpoint) has stayed the same if not increased. My lowest rated starter on defense at any position is around an 80-82.
Most everyone else is mid 80s to low 90s. My offense consistently performs with around 30 ppg, but that creates issues where I lose multiple games each year by 3 pts.
So.. what are the factors that matter MOST to get the talent to turn into wins (especially on defense)?
Most everyone else is mid 80s to low 90s. My offense consistently performs with around 30 ppg, but that creates issues where I lose multiple games each year by 3 pts.
So.. what are the factors that matter MOST to get the talent to turn into wins (especially on defense)?