I don't think Rapid Dragon is designed to be employed in isolation. I would envision it would be used in tandem with other platforms/systems as part of large scale saturation attacks. A weapons system can offer value outside of its direct use, ie causing an adversary to divert resources to counter it. At a procurement level, resources being channeled for R&D and production of ultra long range SAMs to counter Rapid Drston will result in less resources for procurement of other weapons systems. At operational level, more VLS tubes on board 055s/052Ds being dedicated to SAMs to defend against saturation attacks will result in less tubes available for carrying offensive missiles.
Right, Rapid Dragon will likely be deployed with a screen of air superiority platforms in front of it, and some long range surveillance platforms to monitor any emerging threats. Although I think if there is a 300 NM type of SAM / AA, then it would still be able to easily threaten the C-17/130. But on the other hand it would certainly also expose the defense sides own AWACS and ELINT. So it is a cat and mouse game, it's always going to be difficult to know what is involved in operational planning, for such a long range strike mission with an unconventional launch platform.
I am just trying to look at this in a dispassionate way and put on the analyst hat. Seems like the most immediate solution would be something like the quad packing of ESSM-like short-medium range SAM system. Will need to have semi-active + data-link for midcourse correction. Terminal guidance may need something in addition to active radar.
Although cheaper option might be to add a couple more CWIS if they can deconflict easily.