HC, I'd say your description of the FD/AP relationship is reversed: the FD tells the AP what to do, or the pilot, not the AP tells the FD what to do.
ECF do not use FDs so their functionality is incorporated into the AP (in a more appropriate way, I think), however with a/c that have separate FDs, they are independent and can function autonomously from the AFCS system. Take a basic S-76 A model, for instance, with a phase 2 SCAS: no coupling at all, but all the FD info for the pilot.