Styrmyr is not Greenshore! We launched a war of conquest on Greenshore, took Greenshore, stopped and offered Styrmyr a treaty. They had big, friendly dinners with our King, smiled a lot, then tried to invade Greenshore again. I want to launch a new, non conquest, campaign to make them stop. I believe this has a better chance of success than continuing to ask nicely of people who clearly aren't willing to deal year after year while our army is tied up defending Greenshore delaying our revanchist agenda. The people involved may be much the same but it's two different campaigns, distinct in time, place, aims and method.
This is wrong. I'm going to give you the benefit of the doubt and assume you just forgot how things actually happened, we invaded Styrmyr because at the time, Greenshore had stopped existing as an independent polity due to Styrmyr conquering their land.
Here are the actions we took that resulted in the current war with Styrmyr. First the attempt at diplomacy where they threw the feast and had polite talk.
Diplomatic Contact, Styrmyr
Personal Stewards of Nature, Styrmyr
Needed: 6+. Rolled: 95+5=100. Crit Success, bonus to PSN roll.
Needed: 11+. Roll: 1d10 → 6+1=7. Failure
The Styrmyr lay out a lavish feast for Melek Balthazar. The talks last almost a month, but Balthazar leaves without Greenshore. It will need to be taken by force. Once Balthazar is back in Valleyhome he draws up a formal declaration of war with the stated aims of regaining Greenshore Province.
Then the next turn we invaded Styrmyr. Specifically Styrmyr because Greenshore had ceased to exist as a polity at that point.
City Levy, targeting Styrmyr
War Mission, targeting Styrmyr
Needed: Irrelevant, Authority
Needed: 5+. Rolled 26. Success.
This is a war of aggression by the Ymaryn. The Styrmyr have launched counterattacks to retake the land we conquered from them, but they have not invaded us once. While the Ymaryn like to talk about how Greenshore is rightfully their land and not Styrmyr's, it is land that belonged to Styrmyr before the war, a war that is still ongoing with no stop to it so far, and we are occupying. Styrmyr has taken no offensive action against us aside from trying to drive out the Ymaryn forces occupying their land.
In this war, we are the aggressors. We are the conquerors. Styrmyr has not done anything wrong and all they've done is fight back against foreign conquerors who have invaded and occupied their land.
Revanchism as in a determination to retake our pre-khan territories is nigh universal and includes Balthazar. People who are prepared to bring that agenda to a screaming halt in order to opportunistically undo a decision made 500 years ago are an extremist minority. Western Wall tried to assassinate Balthazar and did kill the Heir, they are rebels who aided the Khan, and we need to secure the west flank in order to promptly and effectively attack them. Someone so insistent on turning that action into an imperialist adventure that they will harm the machineries of the state (i.e. cause a game mechanical effect) is sabotaging both revanchism and our response to attempted regicide. If Balthazar doesn't deal with them in the manner of a medieval king then he won't stay a medieval king.
Just saying it works that way doesn't mean that in-universe characters will see it that way like you do. See the recent assassination attempt as even blaming the revanchists for that wouldn't have let us get rid of them.
Saying that the revanchists are sabotaging the war effort doesn't work when the people of the Ymaryn won't see it that way. It could just as easily be viewed as the king failing to properly punish Western Wall for their affronts and then harming the war effort by wasting resources on wrongly punishing noble Ymaryn patriots who just wanted to get the king to properly deal with those dastardly rebels in the north. Or perhaps it would be viewed as these honourable Ymaryn patriots who just have good intentions and just want to ensure the king isn't shying away from inflicting justice on those traitorous rebels, only for the king to be a tyrant who wrongly punishes them to the point of diverting resources from the war effort to do those. Heck, they might even just say that we deliberately provoked the revanchists to get them to rebel instead of focusing on the war effort and they would be right because that is what you are suggesting.
The majority of the Ymaryn don't see the revanchists or revanchists as bad things. In fact, they have popular support amongst the populace. That is why we spent every turn since we stabilised after the Collapse making sure that they were appeased. The QM has repeatedly stated that we aren't just getting rid of revanchism until we retake all of the Ymaryn traditional provinces (Amber Road counts as a distant trade outpost, not a province). There is no quick or easy way to get rid of revanchists. The QM has deliberately set things up so the most painless and swiftest way is to give them what they want by going about restoring the old borders of the Ymaryn Empire.
You voted for the tantrum spiral. And one needs only look at history to see that people can have revanchist claims on land they haven't had for thousands of years. Hell, on land they never had but someone else who lived in the same area long ago did.
Slaying Revanchism will not be easy, nor will it be painless.