Only issue I could see with the bartering system before is you could barter with ANY vassal to sue for peace which seems wrong.
If we could send a emissary or diplomat companion on a mission to barter for peace this could remedied. Add an option to initiate a barter, they return in a few days with the demands of the Ruler and you could either accept or decline.
Is that more wrong than simply declaring peace at any time without anyone on the enemy faction being able to object? I think the best way would be if you press the negotiate peace button and it just 'magically' opens a negotiation window with the king of that faction, regardless of where he is. I know that is not perfect but the current system makes playing your own kingdom just stupid and pointless.
How to easily conquer the entire map without losing a single seige, battle, getting captured or even having a single village be raided in 4 simple steps.
Step 1. Find an undefended castle.
Step 2. Declare war and take the castle
Step 3. Declare peace with that faction
Step 4. Repeat steps 1-3 as many times as needed to conquer the entire map.
Is an enemy chasing you that you can not outrun? Declare peace
Is your capital being siege and there is no way you can defend it? Declare peace.
Did a much stronger faction just declare war on you? Declare peace.
Do you want to take this castle from a faction that is way stronger than you? Follow steps 1-3.
It removes any challenge from the game. In every game I have played; warband, total war, crusader kings.... peace is NEVER unilateral. The AI looks at the state of the war and decides if peace is a good option. In no game (other than bannerlord) can you simply decide to have peace at any time and whenever it is convenient to avoid the consequences of declaring a war or what ever.
I mean it is fine if you are just a vassal because the AI will usually not vote for peace (although this still does not address the issue on why your council can force the enemy to stop attacking your castles) but for making your own kingdom, this is I think the most absurd exploit that no one is talking about.