I'd second what Ironside said, bad morale-reducing vices can do a lot of damage to your army's effectiveness. I have in the past had a 6* "good runner" lose a battle through mass rout, yet when I replayed it using a 2* stand-in (by shifting the original general into the reinforcements) who had no vices or virtues, it was an easy win. If you get as many morale upgrades for your troops as possible (grand mosque/cathedral etc) then it will help to offset some of the losses due to "good runner" vices. By the time your general gets to "doubtful courage" with "retreats often" it's a wonder anyone even turns up for the battle in the first place "Ooh look, the enemy has sent two peasants with a white flag -- RUN AWAY!!!!"