Feels like you are creating regional scenarios to fit a line of argument. China's a big place but the reported range of the Y-20 is 4500km with a full load this allows it to go pretty much anywhere within China with range to spare (Harbin to Lhasa and Harbin to Hainan are both ~3500km) so within the Chinese borders and pretty much anywhere considered "regional" it doesn't need in flight re-fuelling or reducing payload, including round trips with full load to the SCS islands. In terms of "Global" missions China is not the USA it's not about to ship half its army to the other side of the world to start a war. Form follows function when they start sticking refuelling probes on Chinese transports then expect the PLA's function to be in "transition".
I suggest we not undersell China's ambition, China has every intention of competing with the US on every playing field, China will be adding refueling as a priority, especially when we consider Africa, and similar missions.