I'm not sure what you mean by "true on the door tag it means absolutely nothing in terms of real world weight carrying capacity".
Real world = the trucking world where the payload stickers, or its GVWR, is not used to determine a overloaded truck. Just axle/tires.....or a registered weight if your state has one. Some like Mine doesn't.
Example only....Using the same trucks you mentioned shows the 6.2 gasser rear axle has a whoppin' 49 lbs more payload capacity than the same 6.7 truck.
The payload sticker is a GVWR based payload.
Some (not all) trucks rear axle can be overloaded by placing all the payload in the bed.
Example...one poster bragged his new 2500 chevy 6.0 gas with a 6200 RAWR had a 3640 lb payload. These trucks rear axle may weigh in the 3000 lb range....now add 3640 lbs in the bed = 6640 lbs.
RAWR can be the lessor of a wheel....tire....rear spring pack.
All this is why we say use the trucks real world payload (RAWR) as our truck campers....GN or 5th wheel pin weight....bumper hitch loads.....RR ties from the farm and ranch store/etc are in the bed over the trucks rear axle.
