The primary problem with the stock intercooler is it's lack of mass. It heat saturates in very short order. The more mass an IC has, the more heat it can soak up.
In real world driving, or on a road course, you need that mass to suck up heat during your brief moments of acceleration, then during your times of part or no throttle, the airflow pulls that heat away.
Yes the stock IC sheds heat quickly, but it has almost no ability to hold it, so it saturates almost instantly.
This is a gross oversimplification, but it gets the point across.