History is dicey. I think people overestimate how much of a single narrative exists, and underestimate how much is a good guess based on fragmentary sources. (There are, of course, very bad guesses based on fragmentary sources). They overestimate the continuity of peoples and cultures (forgetting that in most places people juggle multiple languages, cultures and even religions). Sukhothai, for instance, certainly existed, but was one of many city-states in the area; its designation as "the origin of the Thai nation" is a nationalist one. Same with its leader (and my profile pic). Srivijaya might not have existed at all outside of a city-state, and accounts of its splendor might be conflating other powers in the region. But were you to go onto a Wikipedia page or pop-history bit, you'll have someone saying authoritatively what places like that were, what life was like, etc. Archaeology tells us where people were and what tools and food they had (but politics and culture have to be inferred), travelers' accounts tell us what visitors thought was important (full of incomplete or biased information), and inscriptions tell us what rulers or those who could write (in durable materials) wanted to record. A frustrating thing about a lot of Southeast Asian ancient history is that people love writing religious texts about the lives of the Buddha, but not a lot about what peasants were eating.
So, for Khmer, for instance, the discovery of the sheer size of Angkor was surprising, because we were relying a lot on inscriptions (the empire from the vantage point of the ruler) and travelers' accounts (the empire from the vantage point of a foreigner). And then when LIDAR came along the scale of Angkor's urban cityscape was shocking - neither Jayavarman nor Zhou Daguan (ruler and visitor, respectively) had thought it important to mention.
That said, what's your objection to these videos? I haven't really watched them (traveling right now).