Range + Speed = Self Deploy = V-280
With the V-280 speed and range, why would you disassemble it, haul it piece by piece into a C-17, and then reassemble it? Like the V-22 tilt rotor the V-280 can self deployed to its destination any where in the world with ferry tanks and inflight refueling. And unlike conventional helicopters (or the Defiant), the V-280 risk of a rotor chopping off the refuel drogue, or its own refuel probe is far less. A cruise speed closer matching the refuel aircraft is also a big advantage.
Remember a primary goal of FLRAA is to give the US Army independence from the Air Force and Navy to deploy its aircraft.
Note, to get the Defiant into a C-17 for transport, the main rotor gearbox needs to be removed. Not a minor task. Not to mention having the hoist required to reassemble the aircraft, unless you plan to haul it in the C-17.