Morale is more of a determinant of individual battles than Discipline/CA due to the following:
What Discipline/CA is better at compared to Morale is depleting the enemy's manpower.
- Morale damage is scaled higher than casualties. All else being equal, a unit that starts at 100% strength and Morale will break at 40% strength.
- Maximum Morale affects both offense (the amount of Morale damage dealt) and defense (the amount of Morale damage that can be received before breaking). Meanwhile Discipline/CA only affects offense.
- It's easier to get large Morale bonuses than large Discipline/CA bonuses.
What Discipline/CA is better at compared to Morale is depleting the enemy's manpower.