This is going deep down the Rabbit Hole,, but it would seem that some major functions of the GPS are based on the incorrect assumption, that thr GPS relied on data FROM the Nav Receiver, to determine it's display of it's Database information.
Taking on of the simpler Garmin GPS system as an example - ie GNS530
Ref: Garmin Trainer - When the GPS is displaying information about VORs, ILS's, etc, it's should be displaying that data based on GPS information, and NOT from any data that would be got from any Nav receivers.
It should not matter if the Nav radio can pick up one of these Nav Aids or not, the GPS should only display information from it's database.(+ aircraft GPS position)
Example: DIS (Distance) to VOR
This should be the Horizontal distance between the Plane's Position, and the Position of the VOR.
GPS gets Plane position, and then looks up in it's Database the Position of the VOR, and displays the Horizontal distance ( not the slant Range : DME)
It also does not care if that VOR is being received by the Nav Receiver, it is in range or out of range, or even if the VOR is Down, or the Nav radio is OFF. (or of course, tuned to a different VOR frequency !)
If the GPS is told to display the closest VORs, it should search its Database, and list the nearest, with number of VORs displayed limited either by number or physical distance.
If the VOR is Low Altitude, with a short range, and the plane is outside that range, it should still display that VOR, if it meets the Number / physical distance rule.
Currently, if the Nav Receiver cannot receive that VOR, it is ignored in the List.
If it is an ILS, and the plane is outside the ILS cones, then it does not display that ILS - which is also incorrect.
Another Example. A DME (no radial information info)
The Gps should display its Distance AND GPS bearing. It does not care that the DME does not transmit any Bearing information.. once again, its NOT considering a Nav Receiver input, its purely displaying the GPS position of the DME Navaid. Distance and Bearing from the Plane.
In fact, the more one looks at the GNS530, comparing it to the true Garmin (Ref: Garmin Trainer - The Garmin Pilot's manual can be ambigeous on some of this ) , the more the operation of the ASOBO MSFS GNS530 is not following even the basic functionality of the real GPS.
So the questions are:
(1) Am I correct, or have I entered the Twilight Zone.?
(2) If it is in fact the modeling of the Garmin is incorrect, does it matter. ?
(3) Should it be corrected, or left to some 3rd Party Mod to make corrections. ?