IMO, Y-20B MRTT is good enough to refuel fighter jets which will likely make up the bulk of refueling missions in a pacific war. The two dozens of YY-20As is enough for special aircraft refueling however most KJ-500s and H-6 don't have the refueling probe hence majority of special aircraft would be KJ-3000, H-20, future large transport, and maybe some very large UAVs.The MRTT variant requires a complex conversion process if a mid-air refueling point is set up in the configuration. Building a dedicated refueling aircraft can avoid this issue and also allow for the loading of more fuel. Additionally, the landing gear compartments of the YY-20A and Y-20 (I'm not entirely sure of the technical term for this area) also differ, which may impact aerial refueling for large aircraft such as the KJ-500A and H-6N (as well as the future KJ-3000).