Well, I suspect this can't be advanced at all.
I completely disagree with you and think this is a once in a lifetime chance for Arcaea to finish Arcachon off and even then it's going to be a hard, brutal, slog. By the end of next winter Arcachon will be refortified and go back to being a nightmare campaign with very little payoff and everyone else opening the money-taps again.
There are likely fundemental back-end parts of our decision trees that diverge somewhere and without everyone laying out every assumption in some tedious philosophy class type structure, it's not going to be resolved. I suspect it's something around the "Can Arcaea sustain a very long stalemate war effort with Arcachon?" or some modification of that, but it may be more fundemental, such as what attracts/retains nobles in a realm.
Yes but in the situation you highlight, the stalemate situation has been affected by OW. I would be entirely possible to make gains against Arcachron that would help in preventing the stalemate situation from being re-established while also diverting against OW. In all likelyhood military action might not even be needed against OW, depending on what sort of political pressure Arcaea could bring to bear against them
Also it seems you argument takes into account OW attacking now, which can't happen as the soonest this theoretical OW action could take place is in one month. By that stage Arcaea has either made gains against Arcachon from the current situation or they haven't, the opportunity will have passed if they haven't.
