Our endocrinologist won't put our kids on Dex.  He said that Dex was "the heavy artillery" and he wanted to use Cortef while he could so he could have something stronger to go to when necessary as they get older.  Then again Jake is 3 and Savannah is 2 months.  Your son is quite a bit older and might need the stronger meds.  He did mention the same thing you said though about Dex needing much more monitoring than Cortef because it is stronger.