on this era fords not all the ECU terminals were gold plated...
"This era"? We're in a forum for '66-77 Broncos. There were no ECUs (nor EECs nor SRS nor ABS) and no Gold terminals in this era. But in the era of Gold terminals - yes, you're right that not all terminals got that plating. Only those in circuits that would benefit from it, and they did - grease isn't necessary with Gold plating.
...XG12 is a lubricant to resist the wear...
Where are you reading that? Certainly not on the packaging nor the MSDS nor any TSB. TSB 98-24-06 only says it's to prevent water corrosion.
...XG 3-A , really only intended for high voltage secondary circuits...
Dielectric grease is not intended for any circuit of any voltage. The main function is to prevent grounding (which might produce ground loops or shorts) between components & heat sinks. That's why it has sand. It's only used on spark plug boots to prevent them adhering to the spark plug ceramic, and to repel water (also in the distributor cap), but it is not to be used in the spark circuit at all. It's recommended on the rotor tip in the distributor, but that's not a contact - it's to reduce the metal's exposure to the highly-corrosive ozone generated by all the sparks. The spark easily blows a hole through the grease where needed so it doesn't interfere with that circuit.
XG12 was never intended to be used on high current terminals...
I haven't seen any documentation about any upper current or voltage limit for XG12. Do you have a link to that? There IS a lower limit published in TSB 98-24-06 that says not in switches BELOW 0.1A@12VDC. That implies that there's no restriction against high-current terminals.
...the 2g fix was an improved heavy duty connector to replace the original , TSB 96-21-4 also no mention of XG12 in that TSB,,
That TSB doesn't mention a heavy-duty connector any more than it mentions XG12. It only mentions that the connector must be replaced if the terminals show damage. But the new replacement connector is NOT claimed to be improved in any way - it's just new. But TSB 98-24-06 says "ACTION: Add the new grease during electrical connection repair," which would apply to the 2G alternator connector.