Old skirts were made of thick material with multiple layers, and crinolines/hoops kept all that heavy stuff off your legs so you could walk freely. Outer skirt layers were then worn outside the corset so they sat on all the scaffolding and not directly on your body.

I understand that, what I'm gettin at is, I don't understand how that would end up interacting with the areas of the back that the corset would be supporting ( basically T7-L3 on this chart going by the sources you gave me), since all that weight would be anchored at the top of the hip-bone. I'm just not seeing how the mechanics of it line up.

Bone-inlaid corsets could also be used like backbraces for heavy work, which is why poor women in some periods would wear them at their jobs and not just at home.

This part though makes more sense to me, as that's kinda how belts work. They're supposed to assist in keeping the spine in a neutral position when picking heavy things up off the ground; although belts aim to achieve this by making it easier for the lifter to generate intra-abdominal pressure in order to maintain a stable posture, whereas the corsets seem to just use hardpoints to both carry load directly, and to force the wearer to maintain a specific posture.