It seems to me that the available information can lead to many different conclusions. For example:
Was the bank the UA 767 executed a "brilliantely executed" "slip" to "inflict maximum damage"? Or was it a desparate bank to actually hit the building, when the terrorist feared he might miss it?
Was the reported 270 degree turn executed by the AA 757 before hitting the Pentagon a "fighter-like" maneuver? Or was it a second approach made necessary because the pilot missed the first one?
Either interpretation would be consistent with the evidence as we know it so far. We shouldn't discount the possibility that these nuts (to use the most polite word that comes to mind) had little more than a PPL (for basic flying skills) and some MS Flight Sim time (from which they could have learned the necessary instrument layout and use -- some of the instrument panels are amazingly detailed and, I'm told, accurate).
And if we're using turning off the transponder as evidence of their having had in-depth training, bear in mind that only one of the four flights (the AA 757 that crashed into the Pentagon) seems to have done so. Plus, turning off the transponder isn't hard -- all you need is to think to do it, and know what it looks like.