If I'm interpreting parent correctly, they're arguing that had the Chinese recently visited the Americas, the Portuguese and Spanish would have encountered native populations which were already decimated by disease. As this isn't the case, the epidemiological argument against shortly prior Chinese encounters with American populations is strong.
That post Portuguese/Spanish contact native American populations were annihilated by disease is now well established fact. That again argues against earlier Chinese contact.
>native American populations were annihilated by disease is now well established fact
Conveniently formulated historic fact absolving settlers IMO. Apropo to topic.
Convincing argument from indigenous is that indigenous in NA didn't get wiped out "because of" disease, worst historic pandemics wipe out like 50% of population over ~10 years before some sort of immunity kicks into population and gen pop rebuilds a few generations after that. Indigenous NA got wiped due to generations of increased deprivation enforced by settlers over 100+ years that made them suspectible to disease/fatality. It's like how malaria, dysentery, starvation was primary cause of death in prison camps, but really it's the fact that prison camp conditions allowed those diseases to spread in enviroment of artificially sustained deprivation.
90% population wipes over multipe generations isn't how disease operates, it's not natural epidemiologic behavior on continental scale. 90% population wipes happens because of coordinated genocide over generations across continent, blaming "contact" and "disease" is deflection. Hence if prevous visitors (can be whoever) didn't stick around for 100 years to coordinate a genocide, the indigenous people would still be around to greet Portugese/Spaniards, because they would have had ~100 years to recover/rebuild from whatever contact disease from prior meeting.
And those populations would recover within few generations, like every other continental spanning peoples that's dealt with small pox since 1500BCE and before. No disease keeps populations across large span of geography at 10% pre outbreak over 100 years. It takes human intervention to force a specific people below replacement level for that long. When smallpox epidemics explodes, it wipes out 50%+ within a few YEARS. And then population RECOVERS, within a few generations. Populations develop some level of immunity OR social learned epidemiological responses to curtail outbreaks. Of course disease can kill, but it does not explain why indigenous population levels did not recover, especially on multi generational timelines. Not debating whether disease increases mortality, but saying disease is cause conveniently ignores the fact that persistent deprivation maintained by settlers over generations caused conditions where disease spread/has increased lethality, combined with repression prevented indigenous populations from recovering.
So yes, IMO it's completely debatable 90% of population would STILL be wiped out after 100 years in event of an earlier, pre Columbian exchange where new disease is introduced to the continent. Because unless those visitors stuck around and active took effort to genocide the locals, but using disease as a weapon AND creating conditions where disease can proliferate without response, local population would recover after multiple generations (european population took ~80 years to recover from black death).
Only if spread continental scale which implies prolonged exchange. Otherwise can be isolated to small cohort. You claim there would be 10% population in prior disease exchange. You claim it's not debatable. I use too much words demonstrate otherwise. You seem to agree. Useful information was exchanged.
That post Portuguese/Spanish contact native American populations were annihilated by disease is now well established fact. That again argues against earlier Chinese contact.