My point is that they see different loads. In more robust conditions in a seaway, where you have a rudder angle which is not amidships. A cat in staying pretty "level" does so by constantly settling -- thats even accross both hulls or any of its appendages. Sometimes, even on larger cats, theres a "snaps'. Thats short roll that has to be resisted -- it can't be resisted evenly vertially or hoziontals or in time. That seeking of balance produces different loadings as the system seeks equialibrium. The effect is not even on the appendages or moving or fixed control surfaces.

I would think that almost no dynamic objects in dynamic environment experience uniform anything.

I'm not sure what the percentage difference might range from in conditions -- but they are not the same.

Beyond when the boat is not moving at all in still water (when nothing measurable is moving) the loads are clearly going be pretty close. Similarly, on relatively flat water, with both hulls "imbedded" in the water about evenly and the boat moving with the rudders amidships you are probably closer to even loads. But put the boat in a seaway with one hull being loaded more, the rudders not amidships to average a course, etc. -- nothing is even.

Equality, after all, is a mathematical abstraction rather than a reality in nature.