First, our Intrigue score isn't in the right place to be doing missions at all. Judging by other stats, it is reasonably likely that the effectiveness of any intrigue action depends on an intrigue score - and our current intrigue is rather flimsy. And taking a Mission actually compounds the problem, because it makes our Intrigue score lower.
Or, maybe the stat that can't be overflowed into, is a more focused form of another stat, and costs said stat to build, is like the other stats we have seen in this area.
You know, the ones that matter at numbers as low as 4 or 5 at the moment?
Second, the Highlanders are a terrible target for our first Intrigue mission. If we want to send an intrigue mission against someone, can we NOT send it against the nation that practically invented Intrigue?
Oh hell yes. Though I'd argue that we'd have a shot if our Intrigue is at least two digits, right now it's just plain suicide. We've our hands full just DEFENDING.
Infiltrating a xenophobic theocracy is hard.
If only they had recently gone through a major religious upheaval, rewriting vast parts of their society, and then attacked every single one of their neighbors they could and then proceeded to completely oppress any sign of rebellion among said neighbors.
If something like that happened, then the complete and utter turmoil caused by such an unfortunate chain of events would make infiltrating them so much easier! We can't be that fortunate however.
I mean, the only way it could be better if one of those neighbors bordered us, knew us for being genuinely chill, and had terrain that we were both intimately familiar with and many paths of travel that would require a significant border guard to cover completely.
Well, even if all of that was true, it would probably still be better if we had some sort of stealth specialist with centuries, preferably millennia of experience that could safely travel throughout the area.
Unfortunately not a single one of these things is true!
Oh, wait.
You want to avoid war with the Highlanders? Start by setting up a rumor mill to figure out when we can pressure them to become more open minded.
You want to prepare for the inevitable war with the Highlanders? Start by setting up a rumor mill to figure out what they're up to and their troop movements.
You want to get better at infiltrating foreign polities? Actually start infiltrating foreign polities, preferably ones that are close and that you aren't worried too much about pissing off if you get caught.
This isn't some sound and safe strategic plan. This is the player in a strategy game refusing to scout their enemy and thus able to get caught with their pants completely down. This isn't a super risk adverse strategy. This is a handful of stats that are inconsequential in the end compared to what they would gain if they succeeded, and will only be slightly missed if they fail.
To be so completely and utterly adverse to trying to practice and leverage a tool as strong as intrigue is to completely and totally invite all surprises and disasters that could befall us when we could have seen them coming a mile away.
Trying is not the height of arrogance. Not trying when the costs are so low and their attitude towards us pretty much already determined is the height of arrogance. We have barely anything to lose, and the ability to avert or dominate an upcoming war to gain.