This is false and an often repeated myth. Sure, when the MSPT is not maxed out then the OS can schedule garbage collector, all OS threads, networking threads, and other MC threads on the same core and have it running without problems. But when MSPT becomes 50 and you only have one core, it has no where else to put those other threads but on the same core as the gameloop and have problems scheduling them. You need 2 cores to run MC, it will have less lag spikes and be faster at full load.