It is indeed bleak, it’s about the horrific realities of War.
Filler is subjective, typically that term would refer to redundant material, which isn’t the case with that book(granted, it has been over a decade since I read it). More so, it goes on tangents that aren’t related to the Japan/America relationship. It goes into Japan and China, prior to America getting involved there and it gets into how America engaged with dissenters during our Colonial or “territorial grab” era, as well as a few other countries. I think that he gets into the Dutch a bit too.
Academic papers would be a pit more pointed and focused in nature.