To respond to the original question: technique (and I do believe driver technique and skill is much more important than car modifications)
You are correct about terrible understeer on exit. Trail braking does alleviate much of that if you can brake later and rotate the car with the brakes even as late as mid-corner and aim for a VERY late apex in order to return to throttle sooner. That's for longer corners.
For the other most common feature of an autocross course, the slalom, what I've learned from one of the best I've ever seen in awd is to figure out an on-off rhythm with the throttle that matches your steering input. The technique here being to use throttle-lift oversteer to rotate around each cone, then back on throttle to catch and balance the car until the next cone. The throttle input here can be quite aggressive instead of the smooth modulation we're always taught and the car is actually a bit more 'tossable' than you might imagine.
Other than that learning to read the course and maintaining proper vision are the most challenging things. The idea is to find every place you can on the course to increase the radius of the turns and open up space to be on the throttle more of the time.
These are a few of the things I've learned, and I am very much a novice at this still
And most of all, have fun with it.
