Geshrin are the civilian half of the NH-1 series, so I don't understand why they differ so drastically from Yamataians in how they interact with nanomachines and pharmaceuticals.
While Geshrin don't have digibrains and can still scar, the most average Geshrin will naturally be more fit than a Nepleslian/human who works to be fit:
Not saying that Geshrin should be super good, as they're certainly inferior to later civilian NH models. But the most significant improvements the NH-22C brought were a digital brain and being able to float, not how the body's immune system functions.