Does SE Asia have culture?

It appears to me that the countries of Southeast Asia seriously pales in cultural content when compared to their East Asian neighbours. While the Chinese has had thousands of years of recorded history and clical literature, I have hardly seen any done by the Vietnamese, Thai or Cambodians other than ones written in Chinese, by Chinese explorers in SE Asia. And what about scientific achievements? It seems that all the major geographical civilizations like the Greeks, Persians, Hindus, Chinese, etc have made major scientific contributions in the ancient world. What about SE Asia? And dare I say, I find East Asian cultures to be way more refined than those for the SE. Weren't they always more backwards? I remember reading a record from a Ming diplomat to the Khmer empire where he described the people wearing little clothes and having only bare necessities. They didn't have things like chairs or bowls to use. Why does it seem that there is such a cultural divide between East Asia and SE Asia?