They're underwater on Sundaland. The prime area for tin mining in that region is on the Sunda Shelf. The oldest bronze manufacturing/smelting site ever discovered is in Thailand.
Believe me, I am very open to alternate ideas about past history. I just question some of the more extreme claims (electrical systems 3000 years ago?). Big, complex systems require big, complex support structures.
There is a fellow on the net that has alot of alternative archeological theories. There have been things discovered that we still couldn't do. One had to do with a garden somewheres in South America that was decorated with fine filligreed silver and gold ornaments, animals and plant sculptures that are almost detailed beyond description.
Of course, who knows. And something might happen that wiped out a lot of evidence.
A flood, maybe... something like that