Yes that's the gross weight, i.e. carrying its maximum rated load. Personal vehicles are very rarely loaded up to their maximum weight, and mostly are driven relatively empty.

Even driven at gross weight, it's doing 5% of the damage per axle of loaded semi. The semi also has 4-5 axles, so it's more like 2% of the damage of the semi.

Mind you, we're talking here about the most damaging personal vehicle loaded to its maximum weight, and the semi is still doing 50x the damage of the personal vehicle. It's reasonable to say that essentially all road damage is done by semis.