the Aircraft had mechanical linkages combined with an AFCS that had equal authority to that of the Pilot.
I'm not a 139 pilot, but this doesn't sound any different to most AFCS systems, especially with upper modes. SAS has fast acting low authority (5-10%) actuators, ATT has slow moving, high authority (100%) actuators. Neither has the power to not be overcome by pilot input, even if the FTR or trim release do not function.