I know no one who believes in the Hwan Empire you cite. I've met more Americans who believe that people didn't land on the moon than Koreans who believe in some Hwan Empire. You shouldn't believe that it appearing on the news reflects wider acceptance (see, for example, Fox News). Cheomseongdae is the oldest observatory in Asia, as none of the others remain. So it's not incorrect, and I don't think that's misleading either. Anyone with common sense would know a medieval observatory can't be the oldest ever in East Asia, especially given that China and Korea both had older societies that looked at the stars. And frankly it did far more than just survive. As earlier pointed out, articles see it as a likely part of a science center of sorts in Gyeongju (during Seondeok's time). The overall point of what Cheomseongdae represents remains--the Silla kingdom in Seondeok's time was in its Golden Age of science and culture despite its troubles (much as Athens' Golden Age in Pericles' time came during a time of war too). And there are of course plenty of sources on Sejong and Korea's advanced naval weaponry in the Imjin Wars. As far as China is concerned, they already have a science buff in Civ VI, and that buff became more significant with the eureka nerf in Rise and Fall. So their advanced historical contributions to science and culture are already reflected.