What you're missing is what you've learned, basically nobody with a TC pays attention to the GVWR.
My 11' TC sitting on a Chevy 3500 SRW weighed in at 11,140 pounds, the truck's GVWR was 9,900. I was not over axle or tire ratings and I put thousands of trouble free miles on the rig, some of them towing a boat.
I then upgraded to a 2005 Chevy dually. The same camper put that truck at about 13,100 pounds, it's GVWR was 11,400. Again, I wasn't over the axle or tire ratings. I had the dually tagged for 14,000 pounds.
The 11.5" AAM rear axle in a Chevy dually is actually rated by AAM at 10,200 pounds but in my truck GM only rated it at 8,550. Their rating was largely based on the weight rating of the factory tires. Upgrading the truck to 19.5" rims and tires would have gone a long way toward letting me use the entire 10,200 pound rating of the axle.
Here's two interesting facts for people who think the GVWR is "gospel".
My company bought a new Chevy 3500 SRW in 2015. They normally come with an 11,500 pound GVWR. Ours was ordered with the optional 10,000 pound rating so that numerous DOT regulations didn't apply to it. There was zero mechanical difference in the truck.
If you run regular "passenger car" tags on a truck in VA they are only good for 7,500 pounds. A truck with a 10,000 pound GVWR that weighs 9,000 pounds is legally overweight if it has car tags. That same truck, if it has truck tags and is registered for 12,000 pounds is not legally overweight if it weighs 12,000 pounds.
You made the point better than I could have ever made it. The reason I have not upgraded to 19.5 tires and wheels is because the upgrade itself would add weight. The tires, rims, lugs are the only weak link left on my rig. I have Alcoa rims and lug nuts, pretty; but I don't like them. I want to switch to American steel rims and lug nuts. I will also upgrade to load f tires when these are done. My extra leaf springs in the rear added 750 lbs of lift per side but the springs themselves weighed 100 pounds that's why I don't factor the 750 per side, just the 700. Same thing with the upgraded front brakes they advertised 15% more stopping grab so I just add 10% because of the extra weight of the up-sized brakes. I'm interested to here what you think about this. upgrading versus weight.