Since you claim Bretagne descent, note that the historical Roland was actually Hroudland, prefect of the Brittany March. The actual historical battle was a small skirmish between the Basques and the rear guard of Charlemagne's army. It was Charlemagne's only major defeat. We know all this because they WROTE IT DOWN.
The Franks, on the other hand, were not literate for another half millenia. It is inappropriate to apply standards applicable to pre-literate stories to written documents of an earlier age.
Don't be silly. Of course they were literate. The calligraphic hand known as Carolingian minuscule was invented as a court hand for Charlemagne's court. There were several contemporary chroniclers of the Merovingians, and plenty more writings from the Carolingian dynasty.
And, as far as applying story standards, the tales of Arthur and Merlin are hand in glove with the tales of Charlemagne and the Twelve Paladins. Both were French Chansons, epic poems of heroic deeds.
Still, there's a second source of Arthurian legend ~ over near the Jura mountains there are settlements of people with unaccountably Galician and Breton surnames. They have their own versions plus parts of copies of even more ancient documents from Galicia (which record events going back to 700 BC and maybe even older).