3 auxiliary fuel tanks?
Fuel is payload!
What else can it carry when these 3 tanks are full?
Can the 2 Marines bring full backpacks or does that require a 2nd V22?
Isn't it pretty apparent that they are demonstrating a long-range ferry capability? Let's say you need to bring in a flight of MV-22's to meet an amphibious ready group. Pick up a Marine Recon element (already embarked on an LHD), and fly off the LHD to an inland target too far for the Sea Stallions. All you'd have to do is dump the ferry tanks.
What else does a KC-130R carry when it's auxiliary tanks are full?