My truck camper exceeded the manufacturer's rated capacity of my vehicle.
I sold it to someone else and bought a fifth wheel that doesn't.
I don't think it matters by what definition you're overloaded. If you're over payload, GVWR, GCWR, tire ratings, the rating for either axle, etc., you're overloaded.
While there is probably a significant engineering factor for the vehicles themselves, for tires, I wouldn't expect there to be any. Truck tires are engineered to carry their full capacity for their usable life. I have not and would not ever overload a tire by even a single pound. That is seriously dangerous on a level way beyond overloading the truck itself by a few pounds.
Modern vehicles have tons of power compared to the ones from yesterday. When I started RVing the trucks were slow compared to now so it was easy to know when a truck was overloaded. Nowadays it's way less obvious handling and braking characteristics that are going to be the weak point, because the drivetrains themselves can certainly accelerate a very unsafe load to a really unsafe speed.