hell take oceanic and native/aboriginal for example. we lump most of them all together when in reality half of them never even interacted till the last few hundred years.
Dunno what 'oceanic' means as a human classification. Maui people (Kānaka Maoli) are Polynesians. I for one don't "lump them together". Among the people Polynesians are known to have interacted with before Europeans reached the Pacific are Melanesians, Micronesians and Native Americans (South America).
I'm an Aborigine and certainly groups in Northern Australia had contact with seafarers from the Indonesian archipelago for tens of thousands of years before Europeans arrived. Though the resultant genetic interchange wasn't extensive it's spread across the continent via longstanding contacts between Aboriginal bands.
When New Guinea and Australia were part of the same landmass (Sahul) there was extensive contact between Melanesians and Aborigines and that
is strongly reflected in the genome of modern Aborigines.
The first Australian Aborigines were almost certainly part of the epic 'Negrito' coastal migration out of Africa over 75,000 years ago (20-30,000 years before homo sapiens existed in Europe). They were initially held up in South India (with their most direct descendants now living on the Andaman and Nicobar Islands) by the various homo erectus subspecies that had long existed in that part of the world, but after Mount Toba exploded and devastated the region they were able to move through areas previously denied them and (relatively) soon arrived in Australia.
Since then there have been several instances of genetic admixture from other groups, most notably Micronesians migrating by sea from what's now Taiwan and Makassan trepang traders but also probably from South Indian (Dravidian) seafarers 4-5,000 years ago. And of course most of us now have considerable European and/or wider Asian ancestry too.