It doesn’t. Core 0 has the heaviest load to be sure, but the balance is spread evenly across the remaining cores.
My setup uses a Ryzen 5 3600 on an X570 mainboard, with 32GB 3200 ram and a 1TB NVMe PCIe Gen 4 SSD. The OS (Win 10 Build 1909) and MSFS reside on the same partition.
Post-patch I have seen frame rates in the mid seventies in the Carenado Mooney, and not lower than mid-thirties around KSFO deep in Class B airspace.
GPU is an RX 5700XT.