John Hawks has found that Oetzi has more Neanderthal ancestry than people in Europe today, while Dienekes has found that Oetzi’s extra dose of archaic seems to come from the non-Near-Eastern fraction of his ancestry. So it looks as if the old population of western Europe has a fairly high Neanderthal fraction, maybe 8 or 9%.
At the other end of Eurasia, Australian Aborigines and Melanesians (and the original inhabitants of the Philippines as well) have comparable amounts of archaic ancestry – some Neanderthal, and about 5% Denisovan.
If you look at the map of Southeast Asia and Australia back in the ice age, people would have entered Sundaland from the north. If there were Denisovans living there, modern human invaders would have gradually picked up more Denisovan ancestry as they moved farther in, and the population with the largest amount of Denisovan ancestry would have been that in eastern Sundaland, just as the most-Neanderthal population would likely have lived in western Europe. That unusually-Denisovan population would have been the one that crossed the water and colonized the Philippines and Australia/New Guinea (called Sahul when joined), expanding manyfold in those empty lands. If Hy Brasil or Avalon had bothered to exist, they might have had a surprisingly Neanderthal native population, for the same reason.
Later, various peoples expanded from less peripheral parts of Eurasia, such as the Middle East or south China. They overran the old-fashioned part-archaic hunter-gatherers, and the modern populations in those areas have less archaic ancestry. So today the people living in the Philippines do not have much Denisovan ancestry, nor do most people living in Australia – where the replacement was quite recent. New Guinea is the biggest exception, partly because they developed agriculture independently, partly because the island’s rough terrain. Even so, western New Guinea is now about half Indonesian, and there are plenty more to come.