My 2 cents:
- Lords are using low tier units because they are constantly fighting thus the leveling of their troops cant keep up with the veteran deaths, so they are permanent stuck with level 1-2-3 troops.
- Sieges deal huge blows to all parties, not only in siege they lose twice or more troops than the defenders due to the previous point, but also they are forced to leave some of their troops as garrisons.
- And finally they lose too many soldiers due to lack of food, over limit and low morale.
To fix this AI should:
- Have a minimun truce of 1 year or/and fight and raise armies in summer using winter to level their troops.
- Instead of donating troops, a portion of the army should stay garrisoned until a new owner has been decided (Also healing the wounded)
- Teach the AI to no go over the party limit (that is a risk tactic meant for players) have always a sort of 3 food type that can last for 10 days and replenish them when there is 1 day worth of food.
At least as a basic fix it should work.