No, please, don't bring back this. Your logic is flawed. If you're in a war, you should prioritize on defending your provinces.
You want good logic then? Here:
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¤ Paid Features from Art of War
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- It is now possible to transfer control of a province to someone you are allied with in a war
Prior to patch 1.8, you could dictate whether the AI gives you land or avoid taking land that would create anger with the AI war leader (or someone else). However, the ability to block that is gone now, which has a small but material impact on wars as you can't safely siege out land you don't want without paid content. To a degree, the paid content replaces previous agency, but that agency is stripped unless you get the DLC.
This is a particular problem if you're sieging out a non-warleader opponent, because you can't separate peace them and the AI can give you whatever the heck it wants, but if you don't siege it out then it will build and consolidate more units, substantially bleeding manpower and war exhaustion you might not have to spare.
The option to not take random provinces is already in the game. Transfer the siege to war leader. Keeping the province tells the ai that you have an interest in it.
It's not good to assume everyone has every DLC. If that's an option, then yes you use it. I haven't touched the DLC because patch 1.8 doesn't work, and it's vexing to hear the (substantiated) suggestion that the DLC *might* solve said performance issues, but as a result slogging through the first 50 years a couple times before getting tired of it I've already encountered problems.
The game should work with mechanics on its own merits without DLC.
Don`t get AI alliances then. Alliances should have drawbacks, and the negotiations work both ways, you have the option to decide for AI if you`re war leader. They get to decide if they are.
The concept of "war leader" is idiotic in the first place and having it be the only negotiation method used isn't exactly historical, especially when it ends in a "screw you" peace deal that prevents an ally from forcing gains of his own (possibly/preferentially through separate peace). That design isn't good for the player or the AI.