War weariness in this mod can be extreme.
Especially in multiplayer if the player you try to attack has the zeus statue.
I went to war against a human player with the statue in early modern times. After about 5 turns of battle with quite some losses on both sides but not too extreme given the army sizes you get in those ages war weariness caused an extreme number of unhappy people in my cities. My biggest cities had around 17 extra unhappy people from war weariness in addition to the normal unhappiness. They starved massively while the war had merely started.
That makes the player with the statue pretty much unassailable and since you can't make peace in multiplayer that easily, the unhappy faces stay for a long time even if you don't continue the war actions.
The reason seems to be the combination of the vanilla base war weariness without the vanilla reduction of it in multiplayer in addition to the zeus statue. The result is quite a broken mechanic.