Nah - people are rarely villains in their own mind. It seems that most folks figure that "God is on our side." The result is that a generation or two after a "brave and noble" defeat, songs are written about events. If they are close to the actual story, thats a bonus.
Consider the standard Jacobite fare - Will Ye No' Come Back Again, Hey Johnnie Cope, Bonnie Dundee, Skye Boat Song, Killiecrankie and on and on - Rather than being written by the defeated Scots (Highlanders) MOST are of the "drawing room Jacobitism" of the gentry (Lowland Scots or English) and aristocracy, written well after the House of Stewart was no longer a threat to George and his kids. The remarkable thing about most of these was not that they got stuff WRONG but that they had gotten so much of it RIGHT! These were songs based on legend and lore in many cases where the story was well known, even if the facts were a little hazy.
The same thing happened in the States - some of the best known "Civil War songs" were written AFTER the war was over (eg., Marching Through Georgia). How many newspapers carried the story about the death of the "drummer boy of Shiloh", each written about a different person?
In Irish music, consider the number of Rebel songs written years after the events - Men of the West about the French landing at Ballina is a classic example - as is Father Murphy/Boulavogue, Rising of the Moon and Kelly from Killane. None of them were contemporary to the events and were written after - when it was relatively safe to do so and after the emotions were recovered enough to do so - 10 to 20 years after the events.
Is anyone REALLY surprised about the lack of German music composed about the defeat of Germany in WWII? Rarely is a society so broken as Germany was in battle, and the populous forced to face the actions of the government done in the name of the nation - done in THEIR name.
In the defeat of WWI, they had a noble image of fighting until they could do no more for the Kaiser and the fatherland. In the end, defeat was conceded after a noble resistance - great material that.
If you ignore the fact that the war was the result of a house of cards coming apart and invading Belgium brought Britain into the war against her, essentially reinforcing the French line when the Wehrmacht swept into France and buying time at Mons for the French to stabilize their lines. THAT was what set up the entire long defeat that was celebrated in song after Versailles.
Sorry - did not mean to rant -