Except most of those books were either never written or never gained popularity until decades or centuries after those events actually happened.
In the aftermath of WW1, people genuinely believed Germany started the war and thought the Treaty of Versailles was deserved. A few people spoke out against it but no one paid attention until decades later.
Anyways, I think Edwin is portrayed as a paragon. The tone of the article (which is supposed to be a historical text) seems to portray Callum is a treacherous, heartless bastard, while Edwin is almost depicted as a brilliant politician whose cunning is to be admired. It goes into full detail on the impact Callum's dealbreaking had on Aetoria, but barely mentions what effect Edwin's dealbreaking had on Cunaris other than a transition of power (how many Cunarians died fighting those distraction wars in Kentaur? How much debt did Cunaris acquire over those years? How many aspiring Cunarian officials/commanders lost job opportunities that were bought out by Aetorians? What sort of dealings and betrayals made all this happen?) It dwells on Edwin's strength, his young age, his cunning, his superiority over his ally Jerome, and at no point does it criticize his decision to seize power.
So yeah, this does seem to be a "history written by the victors" case. It may not be on the same level as some other examples from IRL history, but the propaganda is still there.
Or maybe I'm just reading too deep into this. Who knows?
Edit: Also, more evidence that Caius is actually the Earl's son: Callum's nose was massive.