I'm sure their total of six nobles will make an amazing dent in Luria...
Of course six nobles would make a dent. You'd damn near double the size of Morek's expeditionary force. And not only that, just think of all the interesting possibilities you have when you give a realm with Morek's resources, six disposable nobles!!!
Think big! Use your imagination! Stop being all "Woe is me, Barca died, I have nothing to live for".
How much damage do you think would have been done to Luria if, instead of dismantling Poryatown's infrastructure and walking away for Luria to quickly retake the city, Morek had turned Poryatown into a duchy, and then spun off a new realm? Morek has insane amounts of gold and more recruiting centers than I have ever seen. Picture 14 nobles, each leading 1,500 CS of troops, popping up in Poryatown. They take the city. Drop off 21,000 CS of militia. (It will actually be more CS, and more effective, if you split the huge units into several smaller units each.) The rich Morekian nobles send metric craptons of gold to one select person in Poryatown. (And not those wimpy Imperial craptons. We're talking the metric system, here.) That person withdraws all that as gold. Helm appoints them as lord of Poryatown. Eviera appoints him as duke of Poryatown. Duke secedes to create Barca v2.1! Time it right, and it could be done within a few minutes of Morek taking the city.
Suddenly, Poryatown isn't just an isolated Morekian region 1,500 miles from the capital, screwing up the stats of every *other* Morekian region. It's now a separate realm smack dab in the middle of Lurian lands, with nice walls, some nice RCs, and with 21,000 CS (or more) of militia. Those six nobles from Barca form the core of the realm, and can recruit more troops from the local RCs. One of them can become an ambassador, and turn the sympathy against Luria for free, and very effectively, since he's in his own realm as an ambassador. Morek can continue to supply gold and food to keep it running.
It doesn't have to be a "viable" realm. If it lasts for two weeks, it's a smashing success. It doesn't even have to be just Barcan nobles. Maybe you can attract some former Asylonians. Maybe a D'Haran or a Fissoan. And maybe a few Morekians who want to be closer to the front, or want more action. (And yes, they do exist.) Think you could get six? Maybe eight? How about if you could get 10?
Now you force Luria to make one hell of a decision. Allow that realm to stay there, growing stronger and raiding their back, or devote a huge army to trying to root them out. And even if they manage to siege the city, they now have to TO an enemy capital that despises them. They have to BTO Poryatown, basically destroying it in the process. And while they are dedicating that huge army to retaking Poryatown, Fissoa and D'Hara have a free reign to screw up the rest of Luria.
And even if you fail, you've had one hell of a ride. *And* you've shoved a big middle finger in Luria's face. What could be better?