I think the consequences for holdings being occupied in CK2 and maybe paradox games in general is quite lenient without too much long term damage. One way is to create loot events which fire for the commander once a holding is occupied giving the commander various options, like this:
- No looting, no Money gained but no negative consequences
- Mild looting, some money gained by the commander while removing some development from the county and some loss of piety of the commander if used against a county following your religion
- Looting, quite alot of money gained by the commander, significant amount of development lost by the county and more piety loss for the commander if county follow your religion.
- Complete looting, large amount of money gained by the commander, large loss of development for the county and alot of piety loss for the commnader if county follow your religion
- Razing, give stress with certain traits, destroys buildings and give the same amount of money as complete looting with even larger amount of development and piety losses.
This mean you have very good reason to protect your holdings from occupation by building strong walls and armies.
While I agree that the consequences for having territory be occupied are quite low in CK2 and other paradox titles like EU4, I don't really think that your proposal is the best way to go about things. It will likely result in there being lots of lag from the extra events whenever wars are taking place. Additionally, what happens for armies that don't have any commanders?
What makes more sense, at least to me, is if occupation results in devastation and reduced development, and would also either outright destroy some buildings, or damage them so that they need to be repaired. It also makes sense to allow the player/s and the AI to potentially set attitudes for how their armies will act when they capture a province and its holdings.
On one extreme you could set it so that your armies will loot and sack as fully as possible, and razing whatever is left, earning you and any commanders/knights more money, improving your popularity with your vassals, and improving morale for your troops, but also utterly devastating the province, its holdings, its buildings, and its population, leaving it completely ruined for generations. On the other end of the spectrum you could choose to go down a separate route, and avoid any looting whatsoever, resulting in worse morale for your troops but better public order in the province, and ensuring that if you annex the province it will actually be useful, as opposed to potentially taking decades to recover.
Obviously these wouldn't be the only two options, and you could pick other less extreme ones somewhere in the middle. I think something like this would allow you to make real, meaningful choices, and would address the current issues that you pointed to. Potentially it might also be possible to choose other options determining how captured holdings would be handled, so you could choose to ruthlessly sack, pillage, and raze most of your enemy's territory, while avoiding doing any damage to the land you wanted to capture.
