you easily have a 25+ level lord rigth away after a while during your campaign, and very late game it can even recruit level 40 lords directly. They can also be kept near the shores of your own provinces with units, ready to recruit a lord and do what I said above whenever there's a danger approaching that place, which means that you don't need to keep a lord around to protect the area, once again helping with the whole upkeep increase.Д«ut tbh, just the ability to recruit a Lord right next to the enemy with a +12 level is already ridiculous enough to use them.

Sicne they don't count for upkeep, they're also pretty usefull to have around simply to get the treasure at sea without requiring a dedicated lord for that. On top of this, black ark don't count as a lord for the increase of upkeep, so you can 'store' units there, recuit only the lord when you need him, he'll get far more level than normal, and then you'll give him units from the ark right away, and next turn he's ready to do whatever you need him for. Just saying, recruiting a lord with a black ark gives soemthing like +12 level to the lord, on top of any faction wide level bonus you can get.

Warhammer 2 black arks