In all fairness, if you display a picture of Cosmos next to Sarah, even if you don’t have the actual in game evidence to support it, they are near identical save for some celestial flair tossed in. If you look up the lore of World B, narratively speaking, the threads tie together at the commencement of the Cycles of War following the pact with Shinryu.

It’s long been theorized that in order to stop the time loop of FFI, it wasn’t a matter of defeating the Fiends or even reaching Chaos but that the Cycles of Dissidia were somehow involved. That is to say, if Jack becomes Chaos and travels to World B to begin the cycle, the cycle can truly end in World A because the reincarnation is halted. very speculative theory mind you but growing strong every day in validity.