Both layout have both components access to fresh air. Sandwich case still have one chamber.
If one have a better temps than the other it will be imo based on how it exhaust warm air
However recycled air (in sandwich cases) don't affect the other due to fresh, or even recycled, air being on opposite sides. Additionally in console style cases(specifically in vertical orientation) as heat rises, the CPU would be hotter (theoretically). In a horizontal orientation both the CPU and GPU have access to either fresh or recycled air from the other component.
Although there are holes in the spine and the 2 compartments are not sealed from one another, I would think it would still be considered dual chamber.
(I could be wrong in some, if not all of my points, but theoretically it makes sense to me. #provemewrong ? jk)
I do agree fully with your final point. It does, ultimately, come down to how effectively any specific case can remove warm air. Great example would be the Node 202 vs the ml08 (I think that's the right one.... It might be the Silverstone raven.... Regardless) both have the same console style layout with opposite facing components, one of which has better cooling for it's GPU due to better/different fan placement in the GPU compartment.