In patches prior to 1.5, shield armor values were incorrectly calculated. Units with massive shields (Dismounted Knights) died as fast as peasants. The 1.5 patch corrects shield defense against both melee and ranged attacks.
If you are running 1.5 on a modern PC, consider these community-verified tweaks: medieval total war 2 15 patch verified
: Resolved issues where the family tree would disappear after a princess married a general who became the Faction Leader. How to Verify and Install In patches prior to 1