The reason the Amerindian population was so weak immunologically, was its extreme inbredness. Over 90% of all American Indians, from Alaska to Tierra Del Fuego, are descended from just four women.
While the separatists are technically wrong, and boats were landing here or there all the time, most of those people just starved, perished, were murdered where they landed.
The boaters had major cultural and religious effect, but were few and male and could not much impact the genetic picture, nor could their small craft be packed with enough artifacts to convince all of today's skeptics.
Yet genetically it is the diffusionists who are wrong, and the whole aboriginal population of both continents and the Caribbean too, is still basically descended from a single boatload of Asians, apparently with just four breeding females, that landed in SOUTH America in a time of high antiquity indeed, some 35 to 39.5 thousand years ago.
It may well have floated with the clockwise current around the Pacific rim from the Sakhalin/Korea area all the way to Chile before finally coming ashore. See Monte Verde, Popiapo, etc.
How do you explain Luzia? (post #58)