Greg Esres wrote:

The airlines have been flying the RNAV overlays of the conventional
terminal routes on an ILS for over 20 years.

What the airlines do is irrelevant to General Aviation operations.
They're using different equipment and operating under different rules.

The different equipment does pretty much the same thing as a Garmin
400/500 series, at least as to LNAV. And, the rules pertaining to air
carrier navigation in the national airspace system are the same rules you
use.

Or, if you think I am wrong, provide specifics.