The point is that 20th century anthropologists & historians had access to significantly less information and first hand experience than those in the 19th century.

In 1800 there were between 50,000 - 100,000 Marquesans. By 1902 there were 3,963.

> It is entirely reasonable to expect evidence of extraordinary claims before accepting them as genuine.

I would say that the Polynesian inhabitants of Aotearoa New Zealand, Ha'waii, and Rapa Nui/Easter Island are all the evidence one needs.

That is indeed evidence they got there by boat, although before DNA comparison it wasn't clear where they came from. (DNA sequencing has revolutionized determining where people came from and who various groups are related to.) It is not sufficient evidence of repeatable navigational skills. Setting out in a boat and luckily happening upon an island is very different from reliably navigating back and forth.

There are modern examples of people in lifeboats drifting incredible distances in the Pacific, with zero navigation.

People didn't accept that the Wrights had flown, either, until the evidence was indisputable. And rightly so, as it was an extraordinary accomplishment.

> It is entirely reasonable to expect evidence of extraordinary claims before accepting them as genuine

In this case, we have the evidence. It's not a theory, the Polynesians are already on all those islands.