i am for the reason that air planes that loiter are not an important staple of the allied arsenal and second the doctrines that have loiter units generally have arty or units that can quickly clear out an okw truck.
of the 3 usf doctrines that have loiter 1 has the calliope and the mechanised doctrine has arty at his disposale that has a good chance of 1 shotting the truck. only airborne is screwed,
The only thing I saw consistently being shot down are the supply drops from Land Lease. IL-2s and P-47s seem to be less vulnerable to the FlakHQ, they still deliver most of their payload while under fire from it. The strafing runs from Tactical Support and such are directional, so just avoid the Flak.