Agreed,two different style builds. Those that are milder using the body and cage as one structure. And those trying to be as light as possible being 25.5D compliant. The sheet metal is merely visual and not much structure.
Doug

I disagree. SFC IMO mainly improve/shortcut the original torturous load path of transmitting forces from the front leaf spring mount, to the rear torque box, to the outer door sill, to the front torque box, to the TB cross member, to the front frame longitudinal.

The original designers were forced to made a number of compromises.

Differences in wall thickness affect stiffness (bending resistance) in direct proportion: .120" wall is 33% more than .090", etc.
The vertical dimension is far and away the most important. 3" tall by 2" wide is 90% more rigid than 2" tall by 3" wide (47% stiffness is lost by rotating).