To put it more simply (maybe?). We generally view the scenario as a statics calculation, simple moment diagram.
At some point, one would think the ratings were derived from taking dynamic loading scenarios into consideration, and they have been. To what extent? Who knows.
But the angle of the vehicle does come into play. Not hugely, as a couple degree difference in angle, still has only slightly less vertical components and a very small horizontal component.
Now add in dynamic loading, hitting bumps and dips at speed, how much does the suspension absorb and what are those stresses on the suspension vs how much load is momentarily added or taken away...
None of us know that, but the fact of the matter remains, there is a practical limit and dissecting that seems to be a popular past time here. Which is contrary to the entire rest of my almost 49 years on this planet, 33 of which have been driving and alot of towing.