North America in 1600 for instance was a mess versus 1500; the English colonists often found whole towns abandoned due to plagues having decimated the peoples living there just handfuls of years before they showed up--traders out of the Spanish and other southerly colonies tended to plant the seeds of destruction on the coasts.
This is what makes me wonder if native genetics and preservation of parts of native culture in North America might have been greater if the DeSoto expedition actually turned into a conquest, followed by setting up a Spanish ruled Kingdom, Spanish settlers, etc than the "hit and run" job it was in OTL.
In other words, although it is in many ways a miserable racial caste system with exploitation, maybe Europeans sticking around and organizing the local hierarchy, any hierarchy, is better for preserving more of the genetic lines and for documenting culture than for the Europeans to pass through, spread devastation and disease, then leave and have hierarchy and specialization totally collapse.
Just trying to figure out here why the Aztecs and Inca and Maya and Guarani and Tupi are fairly central to the identity of modern Mexico, Peru, Guatemala, Paraguay and Brazil, but the Mississippians are an obscure footnote to US history.
The other advantage of a Vinland contact is diseases won't hit in repeated tsunamis, multiple hits in a single generation. The major contact point will be Iceland, which was simply too small to support epidemic diseases. So smallpox, for instance, did hit, but was often a couple of centuries between epidemics.
With Old World entry into the new world limited by a bottleneck in Iceland for several centuries, I could see the Amerindian Norse be very, very susceptible to diseases from later waves of migrants.
This could result in their Vinland societies being overrun by conquerors from more "crowded Europe".
Also, maybe Vinland could try to develop some quarantine practices (not that these would work), like the idea of buying Africans from Portuguese might be a neat way to get more grain planted and churches built, but diseases come soon after, so Vinlandic communities boycott the slave trade for that reason.