Tire width in the popup tool tip doesn’t match the width of the tire setting.
The max load of the tires can easily be lower than the max load rating plus the vehicles weight. Set to where it still has some drivability, select progressive or higher, preferably hydrodynamic.
With the cargo volume of the ute selected (10’s large sedan ute) I would have to fill it completely with stone, water of that volume would only take up half of the weight. Cargo volume does effect it, at a rate of about .5kg per liter, but at just over 3000L the load rating is over 5700kg
The frame type/material/quality doesn’t affect the max load.
My suggestion would be to have the load capacity set by the springs/spring type, but be capped by the tires/cargo volume/(frame type/quality/material)
edit: Heck if you tie utility more to the load capacity it would probably even give a better separation between heavy utility/delivery and the lower utility/delivery markets.