Why is China horrendously underrepresented in WWII discussion?

[True Federalist (진정한 연방 주의자)]

I think there are three primary reasons.

First, including the whole of the Second Sino-Japanese War in World War II means it begins before 1939.

Second, in many respects, the Second Sino-Japanese War is mainly part of the broad sweep of conflict in China that followed the 1911 Revolution rather than part of World War II. It only got tied into World War II because Japan decided to attack the United Kingdom, the Netherlands, and the United States. Indeed, had Japan left alone the United States, they might well have not only succeeded in their attempt to secure the Southern Territories, but kept their conflict from being seen as part of World War II.

Third, there's not much film of the Second Sino-Japanese War.

[True Federalist (진정한 연방 주의자)]

Cold War can explain the underrepresentation of the eastern european front.
But China was ruled by the Kuomitang during the WW2.

Maybe de jure, but a major reason Japan involved itself in China is that some Army officers thought they could take advantage of the conflict between the KMT and the CCP to take control of China.

[True Federalist (진정한 연방 주의자)]

I may be wrong, but it seems the CCP itself has not elevated WW2 into a central part of the national mythos, probably because the bulk of the fighting was done by the Kuomintang.

You're wrong. The Second Sino-Japanese War was a three-sided mess. The KMT certainly had the more traditional forces involved of the two Chinese factions.

[True Federalist (진정한 연방 주의자)]

I may be wrong, but it seems the CCP itself has not elevated WW2 into a central part of the national mythos, probably because the bulk of the fighting was done by the Kuomintang.

You're wrong. The Second Sino-Japanese War was a three-sided mess. The KMT certainly had the more traditional forces involved of the two Chinese factions.

wiki tells me that the ROC lost more than 8 times the men than the Commies did. (1.3M killed vs 160k)  Either the ROC did the bulk of the fighting or the Commies were a lot better at not getting killed (seems unlikely).

Yes, when it came to stand up battles against the Japanese, the NRA did more of that than the PLA. It's a lot easier for a guerrilla force to avoid being slaughtered in an uneven fight. There's also the fact that dying and fighting aren't the same thing.