Somehow I really don't think App Switching in the form of Multitasking on iOS devices is solely restricted performance due to RAM.
Was the storage on each device the same during your application multitasking tests? (non 4K video exporting)
Which applications and size of working files?
I am not sure what you mean here, but I do think ram plays a factor in multitasking considering it is limited depending on the amount of ram a device has.