I think the references to his family and military prowess were full of holes. While he traveled extensively with his children, I have read that they were pretty wild and undisciplined.  The daughters were notorious for sleeping around and getting into trouble.  As for his military campaigns, Eisenhard describes Charlemagne as being patient and never ceasing to reach his goal.  In reality, many of the battles he fought were just unsuccessful and costly.  He kept throwing resources at the problems of rebellious clans until they just moved too far away for his forces to bother pursuing any more.  Eisenhard considered it a victory but it was inefficient method of war.